Physical quantity measurement device for fluid with narrowed flow path

ABSTRACT

A physical quantity measurement device includes a housing forming a measurement flow path in which a sensor support supports a physical quantity sensor. The measurement flow path includes a sensor path in which the physical quantity sensor is disposed, an upstream curved path between the sensor path and an inlet, and a downstream curved path between the sensor path and an outlet. The housing includes a measurement narrowed portion that gradually narrows the measurement flow path in a direction from the inlet toward the physical quantity sensor. An upstream end of the sensor support is provided upstream of the measurement narrowed portion in an arrangement cross section along an imaginary straight line passing through the physical quantity sensor and extending in an arrangement direction in which the upstream curved path and the downstream curved path are arranged.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of InternationalPatent Application No. PCT/JP2019/003955 filed on Feb. 5, 2019, whichdesignated the U.S. and claims the benefit of priority from JapanesePatent Application No. 2018-020388 filed on Feb. 7, 2018, JapanesePatent Application No. 2018-243415 filed on Dec. 26, 2018, JapanesePatent Application No. 2018-246193 filed on Dec. 27, 2018, JapanesePatent Application No. 2018-246194 filed on Dec. 27, 2018, JapanesePatent Application No. 2018-246195 filed on Dec. 27, 2018, JapanesePatent Application No. 2018-246196 filed on Dec. 27, 2018, and JapanesePatent Application No. 2018-246197 filed on Dec. 27, 2018. The entiredisclosures of all of the above applications are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a physical quantity measurement device.

BACKGROUND

A physical quantity measurement device that measures a physical quantityof a fluid. For example, an air flow rate measurement device includes apassage forming member that forms a measured passage in which air flows,and a sensor that detects a flow rate of air flowing through themeasured passage.

SUMMARY

According to at least one embodiment of the present disclosure, aphysical quantity measurement device measures a physical quantity of afluid. The physical quantity measurement device includes a measurementflow path, a physical quantity sensor that is provided in themeasurement flow path and detects the physical quantity of the fluid, asensor support supporting the physical quantity sensor in themeasurement flow path, and a housing that defines the measurement flowpath. The measurement flow path includes a measurement inlet throughwhich the fluid flows into the measurement flow path, and a measurementoutlet through which the fluid flowing from the measurement inlet flowsout of the measurement flow path. The measurement flow path includes asensor path in which the physical quantity sensor is disposed, anupstream curved path provided between the sensor path and themeasurement inlet in the measurement flow path, and a downstream curvedpath provided between the sensor path and the measurement outlet in themeasurement flow path. The upstream curved path is curved in the housingso as to extend from the sensor path toward the measurement inlet, andthe downstream curved path is curved in the housing so as to extend fromthe sensor path toward the measurement outlet. The housing includes ameasurement narrowed portion that gradually reduces and narrows themeasurement flow path in a direction from the measurement inlet towardthe physical quantity sensor. An arrangement line is defined as animaginary straight line that passes through the physical quantity sensorand extends in an arrangement direction in which the upstream curvedpath and the downstream curved path are arranged. An upstream end of thesensor support is provided upstream of the measurement narrowed portionin an arrangement cross section along the arrangement line.

BRIEF DESCRIPTION OF DRAWINGS

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbe apparent from the description and drawings, and from the claims.

FIG. 1 is a diagram showing a configuration of a combustion systemaccording to a first embodiment.

FIG. 2 is a front view of an air flow meter attached to an intake pipe.

FIG. 3 is a plan view of the air flow meter attached to the intake pipe.

FIG. 4 is a perspective view of the air flow meter viewed from a throughinlet.

FIG. 5 is a perspective view of the air flow meter viewed from a throughoutlet.

FIG. 6 is a side view of the air flow meter viewed from a connectorportion.

FIG. 7 is a side view of the air flow meter viewed from a side oppositethe connector portion.

FIG. 8 is a cross-sectional view taken along a line VIII-VIII of FIG. 2.

FIG. 9 is a perspective view of a sensor SA according to a configurationgroup A.

FIG. 10 is a plan view of the sensor SA viewed from a molded frontsurface.

FIG. 11 is a plan view of the sensor SA viewed from a molded backsurface.

FIG. 12 is a perspective view of a flow rate sensor.

FIG. 13 is a diagram showing a wiring pattern of a membrane portion.

FIG. 14 is a vertical cross-sectional view of the air flow meter.

FIG. 15 is a cross-sectional view taken along a line XV-XV in FIG. 14.

FIG. 16 is a cross-sectional view taken along a line XVI-XVI in FIG. 14.

FIG. 17 is a vertical cross-sectional view of an air flow meter around ahousing partition according to a configuration group B.

FIG. 18 is a view showing a state before a sensor SA is assembled to ahousing.

FIG. 19 is a plan view showing the housing before the sensor SA isassembled.

FIG. 20 is a view showing a state before the sensor SA deforms a housingpartition of the housing.

FIG. 21 is a view showing a state after the sensor SA deforms thehousing partition of the housing.

FIG. 22 is a vertical cross-sectional view of an air flow meteraccording to a configuration group D.

FIG. 23 is an enlarged view around a sensor path of FIG. 22.

FIG. 24 is a cross-sectional view taken along a line XXIV-XXIV of FIG.22.

FIG. 25 is an enlarged view around the sensor path of FIG. 24.

FIG. 26 is an enlarged view around the sensor path and a verticalcross-sectional view of the air flow meter according to a configurationgroup E.

FIG. 27 is an enlarged view around the sensor path and a horizontalcross-sectional view of the air flow meter.

FIG. 28 is a schematic front diagram of an air flow meter according to aconfiguration group H.

FIG. 29 is a perspective view of a connection terminal.

FIG. 30 is a top view of the connection terminal.

FIG. 31 is a cross-sectional view taken along a line XXXI-XXXI of FIG.28.

FIG. 32 is a cross-sectional view taken along a line XXXII-XXXII of FIG.28.

FIG. 33 is a side view of an air flow meter in a state of being attachedto an intake pipe according to a second embodiment.

FIG. 34 is a front view of the air flow meter.

FIG. 35 is a cross-sectional view taken along a line XXXV-XXXV of FIG.33.

FIG. 36 is a cross-sectional view taken along a line XXXVI-XXXVI line ofFIG. 35 according to a configuration group B.

FIG. 37 is an enlarged view around a sensor SA of FIG. 35.

FIG. 38 is an exploded cross-sectional view of a base member, a covermember and the sensor SA in FIG. 35.

FIG. 39 is an enlarged view around a sensor SA of BH6.

FIG. 40 is a vertical cross-sectional view of an air flow meteraccording to a configuration group C and a third embodiment.

FIG. 41 is an enlarged view around a through flow path of FIG. 40.

FIG. 42 is a diagram for explaining a cross-sectional area of an inletpassage portion.

FIG. 43 is a view for explaining a main flow entering the through flowpath.

FIG. 44 is a view for explaining a downward deflected flow entering thethrough flow path.

FIG. 45 is a view for explaining an upward deflected flow entering thethrough flow path.

FIG. 46 is a diagram showing a relationship between an inclination angleof an inlet ceiling surface with respect to a main flow line and anoutput fluctuation of the air flow meter.

FIG. 47 is a diagram showing a change of a flow rate.

FIG. 48 is a diagram showing a relationship between a pulsationcharacteristic and an amplitude ratio.

FIG. 49 is a diagram explaining configurations which are different inbranch angle.

FIG. 50 is a diagram showing a relationship between the branch angle andthe pulsation characteristic.

FIG. 51 is a vertical cross-sectional view of an air flow meter around ahousing partition according to the first embodiment of a configurationgroup B1.

FIG. 52 is a vertical cross-sectional view of an air flow meter around ahousing partition according to the second embodiment of a configurationgroup B2.

FIG. 53 is an exploded cross-sectional view of a base member, a covermember and the sensor SA.

FIG. 54 is a vertical cross-sectional view of an air flow meter around ahousing partition according to the first embodiment of a configurationgroup B4.

FIG. 55 is a vertical cross-sectional view of an air flow meter around ahousing partition according to the second embodiment of a configurationgroup B5.

FIG. 56 is an exploded cross-sectional view of a base member, a covermember and the sensor SA.

FIG. 57 is a vertical cross-sectional view of an air flow meter around ahousing partition according to the second embodiment of a configurationgroup B6.

FIG. 58 is an exploded cross-sectional view of a base member, a covermember and the sensor SA.

FIG. 59 is a vertical cross-sectional view of an air flow meter around ahousing partition according to the first embodiment of a configurationgroup B7.

FIG. 60 is a vertical cross-sectional view of an air flow meter around athrough flow path according to a third embodiment of a configurationgroup C1.

FIG. 61 is a vertical cross-sectional view of an air flow meter around athrough flow path according to the third embodiment of a configurationgroup C2.

FIG. 62 is a vertical cross-sectional view of an air flow meter around athrough flow path according to the third embodiment of a configurationgroup C3.

FIG. 63 is a vertical cross-sectional view of an air flow meteraccording to the first embodiment of a configuration group D1.

FIG. 64 is a horizontal cross-sectional view of an air flow meteraccording to the first embodiment of a configuration group D14.

DETAILED DESCRIPTION

A comparative example will be described below. A physical quantitymeasurement device of the comparative example, for example, an air flowrate measurement device includes a passage forming member that forms ameasured passage in which air flows, and a sensor that detects a flowrate of air flowing through the measured passage. The passage formingmember forms a narrowing portion that gradually narrows the measuredpassage in a direction from upstream of the sensor toward the sensor. Asensor assembly having the sensor is attached to the passage formingmember, and the sensor assembly has a sensor support that supports thesensor. In the measured passage, the sensor support is provideddownstream of an upstream end of the narrowed portion. In thecomparative example, a regulating effect of the narrowed portionregulating air flowing from upstream toward the sensor can be obtained.

However, in the measured passage, when the air flowing from upstreamtoward the sensor reaches the sensor support, the sensor support becomesan obstacle to the air, and this sensor support may cause turbulence inthe air flow. In particular, in the comparative example, since anupstream end of the narrowed portion is provided upstream of the sensorsupport, the sensor support may cause turbulence of air flow duringregulation of the air flowing toward the sensor. In this case, theturbulence of the air flow generated by the sensor support will beregulated by a part of the narrowed portion that is arranged downstreamof the sensor support, but the turbulence cannot be regulated by a partof the narrowed portion that is arranged upstream of the sensor support.As described above, when the upstream end of the narrowed portion isprovided upstream of the sensor support, the regulation effect of thenarrowed portion may be reduced, and the flow-rate detection accuracy ofthe sensor is likely to be reduced. Therefore, the accuracy inmeasurement of a physical quantity such as a flow rate of a fluid suchas air may decrease, and a measurement accuracy of the physical quantitymeasurement device may decrease.

In contrast, the present disclosure provides a physical quantitymeasurement device capable of improving an accuracy in measurement of aphysical quantity.

A disclosed aspect is a physical quantity measurement device thatmeasures a physical quantity of a fluid. The physical quantitymeasurement device includes a measurement flow path, a physical quantitysensor that is provided in the measurement flow path and detects thephysical quantity of the fluid, a sensor support supporting the physicalquantity sensor in the measurement flow path, and a housing that definesthe measurement flow path. The measurement flow path includes ameasurement inlet through which the fluid flows into the measurementflow path, and a measurement outlet through which the fluid flowing fromthe measurement inlet flows out of the measurement flow path. Themeasurement flow path includes a sensor path in which the physicalquantity sensor is disposed, an upstream curved path provided betweenthe sensor path and the measurement inlet in the measurement flow path,and a downstream curved path provided between the sensor path and themeasurement outlet in the measurement flow path. The upstream curvedpath is curved in the housing so as to extend from the sensor pathtoward the measurement inlet, and the downstream curved path is curvedin the housing so as to extend from the sensor path toward themeasurement outlet. The housing includes a measurement narrowed portionthat gradually reduces and narrows the measurement flow path in adirection from the measurement inlet toward the physical quantitysensor. An arrangement line is defined as an imaginary straight linethat passes through the physical quantity sensor and extends in anarrangement direction in which the upstream curved path and thedownstream curved path are arranged. An upstream end of the sensorsupport is provided upstream of the measurement narrowed portion in anarrangement cross section along the arrangement line.

According to the above aspect, the measurement narrowed portiongradually narrows the measurement flow path in the direction from themeasurement inlet toward the physical quantity sensor, Therefore, thefluid flowing from the measurement inlet along the measurement narrowedportion can be regulated by the measurement narrowed portion. Moreover,since the upstream end of the sensor support is provided upstream of themeasurement narrowed portion in the arrangement cross section, the airpassing through the upstream end of the sensor support along thearrangement cross section is regulated by the entire measurementnarrowed portion in the arrangement cross section. In this case, even ifturbulence of the air flow occurs due to the air flowing in themeasurement flow path and reaching the sensor support, this turbulenceof the air flow can be reduced by the entire measurement narrowedportion. That is, decrease in flow regulation effect of the measurementnarrowed portion can be reduced by the presence of the sensor support.Therefore, deterioration of accuracy in detection of physical quantityby the physical quantity sensor can be reduced, and as a result, anaccuracy in measurement of the physical quantity by the physicalquantity measurement device can be enhanced.

Hereinafter, multiple embodiments of the present disclosure will bedescribed with reference to the drawings. Incidentally, the samereference numerals are assigned to the corresponding components in eachembodiment, and thus, duplicate descriptions may be omitted. When only apart of the configuration is described in each embodiment, theconfiguration of the other embodiments described above can be applied tothe other parts of the configuration. Further, not only the combinationsof the configurations explicitly shown in the description of therespective embodiments, but also the configurations of the plurality ofembodiments can be partially combined together even if theconfigurations are not explicitly shown if there is no problem in thecombination in particular. Unspecified combinations of theconfigurations described in the plurality of embodiments and themodification examples are also disclosed in the following description.

First Embodiment

A combustion system 10 shown in FIG. 1 includes an internal combustionengine 11 such as a gasoline engine, an intake passage 12, an exhaustpassage 13, an air flow meter 20, and an ECU 15, and the combustionsystem 10 is mounted on a vehicle, for example. The air flow meter 20 isprovided in the intake passage 12 and measures physical quantities suchas a flow rate, a temperature, a humidity, and a pressure of an intakeair supplied to the internal combustion engine 11. The air flow meter 20is a flow rate measurement device that measures the flow rate of air,and corresponds to a physical quantity measurement device that measuresa fluid such as intake air. The intake air is a gas supplied to acombustion chamber 11 a of the internal combustion engine 11. In thecombustion chamber 11 a, a mixture of the intake air and a fuel isignited by an ignition plug 17.

The ECU (Engine Control Unit) 15 is a controller for controlling anoperation of the combustion system 10. The ECU 15 is a calculationprocessing circuit including a processor, a storage medium such as aRAM, a ROM and a flash memory, a microcomputer including an input andoutput unit, a power supply circuit, and the like. The ECU 15 receives asensor signal output from the air flow meter 20, sensor signals outputfrom a large number of vehicle-mounted sensors, and the like. The ECU 15uses measurement results of the air flow meter 20 to perform an enginecontrol such as control of a fuel injection amount and an EGR amount ofan injector 16. The ECU 15 is a controller that controls an operation ofthe internal combustion engine 11, and the combustion system 10 may bereferred to as an engine control system. The ECU 15 corresponds to anexternal device.

The ECU 15 may also be referred to as an electronic control unit. Thecontrol unit or the control system is provided by (a) an algorithm as aplurality of logic called an if-then-else form, or (b) a learned modeltuned by machine learning, e.g., an algorithm as a neural network.

The controller is provided by a control system including at least onecomputer. The control system may include a plurality of computers linkedby data communication devices. The computer includes at least oneprocessor (hardware processor) that is hardware. The hardware processorcan be provided by the following (i), (ii), or (iii).

(i) The hardware processor may be at least one processor core thatexecutes a program stored in at least one memory. In this case, thecomputer is provided by at least one memory and at least one processorcore. The processor core is called CPU: Central Processing Unit, GPU:Graphics Processing Unit, or RISC-CPU, for example. The memory is alsocalled a storage medium. The memory is a non-transitory and tangiblestorage medium, which non-temporarily stores a program and/or datareadable by the processor. The storage medium may be a semiconductormemory, a magnetic disk, an optical disk, or the like. The program maybe distributed as a single unit or as a storage medium in which theprogram is stored.

(ii) The hardware processor may be a hardware logic circuit. In thiscase, the computer is provided by a digital circuit including a numberof programmed logic units (gate circuits). The digital circuit is alsocalled, for example, a logic circuit array, an ASIC (ApplicationSpecific Integrated Circuit), a FPGA (Field Programmable Gate Array), anSOC (System on a Chip), a PGA (Programmable Gate Array), or a CPLD(Complex Programmable Logic Device), for example. The digital circuitmay comprise a memory storing programs and/or data. The computer may beprovided by an analog circuit. A computer may be provided by acombination of a digital circuit and an analog circuit.

(iii) The hardware processor may be a combination of the above (i) andthe above (ii). (i) and (ii) are placed on different chips or on acommon chip. In these cases, the part (ii) is also called anaccelerator.

The control device, the signal source, and the control object providevarious elements. At least some of these elements may be referred to asblocks, modules, or sections. Furthermore, elements included in thecontrol system are referred to as functional means only whenintentional.

A control units and methods described in the present disclosure may beimplemented by a special purpose computer which is configured with amemory and a processor programmed to execute one or more particularfunctions embodied in computer programs of the memory. Alternatively,the control unit and the method described in the present disclosure maybe implemented by a dedicated computer configured as a processor withone or more dedicated hardware logic circuits. Alternatively, thecontrol unit and the method described in the present disclosure may berealized by one or more dedicated computer, which is configured as acombination of a processor and a memory, which are programmed to performone or more functions, and a processor which is configured with one ormore hardware logic circuits. The computer programs may be stored, asinstructions to be executed by a computer, in a tangible non-transitorycomputer-readable medium.

The combustion system 10 includes measurement units as in-vehiclesensors. As the measurement units, in addition to the air flow meter 20,there are a throttle sensor 18 a and an air-fuel ratio sensor 18 b, forexample. Each of these measurement units is electrically connected tothe ECU 15 and outputs a detection signal to the ECU 15. The air flowmeter 20 is in the intake passage 12, and provided downstream of an aircleaner 19 and upstream of a throttle valve provided with the throttlesensor 18 a. The air cleaner 19 includes an air case that forms a partof the intake passage 12, and an air filter that removes foreign matterssuch as dust from the intake air. The air filter is attached to the aircase.

As shown in FIGS. 2, 3 and 8, the air flow meter 20 is attached to apiping unit 14 as an attachment object. The piping unit 14 includes anintake pipe 14 a, a pipe flange 14 c, and a pipe boss 14 d, and is aforming member that forms the intake passage 12. The piping unit 14forms at least a part of the air case, for example. In suchconfiguration in which the piping unit 14 forms the air case, the airfilter is attached to the piping unit 14 in addition to the air flowmeter 20. In the piping unit 14, the intake pipe 14 a, the pipe flange14 c and the pipe boss 14 d are made of a resin material, for example.

The intake pipe 14 a is a pipe such as a duct that forms the intakepassage 12. The intake pipe 14 a is provided with an airflow insertionhole 14 b as a through hole that penetrates through an outer peripheryof the intake pipe 12 a. The pipe flange 14 c is formed in an annularshape and extends along a circumferential edge of the airflow insertionhole 14 b. The pipe flange 14 c extends from an outer surface of theintake pipe 14 a in a direction away from the intake passage 12. Thepipe boss 14 d is a columnar member, and is a support portion thatsupports the air flow meter 20. The pipe boss 14 d extends from theouter surface of the intake pipe 14 a along the pipe flange 14 c.Multiple pipe bosses 14 d (e.g. two pipe bosses 14 d) are provided forthe intake pipe 14 a. In the present embodiment, both the pipe flange 14c and the pipe bosses 14 d extend in a height direction Y from theintake pipe 14 a.

The air flow meter 20 is inserted into the pipe flange 14 c and theairflow insertion hole 14 b such that the air flow meter 20 enters theintake passage 12 while the air flow meter 20 is fixed to the pipe boss14 d via a fixing tool such as a bolt. The air flow meter 20 is not incontact with an end surface of the pipe flange 14 c, but is in contactwith an end surface of the pipe boss 14 d. Therefore, the relativeposition and angle of the air flow meter 20 with respect to the pipingunit 14 are set not by the pipe flange 14 c but by the pipe boss 14 d.The end surfaces of the multiple pipe bosses 14 d are coplanar with eachother. In FIG. 8, illustration of the pipe bosses 14 d are omitted.

In the present embodiment, a width direction X, the height direction Y,and a depth direction Z are defined for the air flow meter 20, and thosedirections X, Y, and Z are orthogonal to each other. The air flow meter20 extends in the height direction Y, and the intake passage 12 extendsin the depth direction Z. The air flow meter 20 includes an inwardportion 20 a positioned in the intake passage 12 and an outward portion20 b protruding outward from the pipe flange 14 c without being in theintake passage 12, and the inward portion 20 a and the outward portion20 b are aligned in the height direction Y.

As shown in FIGS. 2, 4, 7 and 8, the air flow meter 20 includes ahousing 21, a flow rate sensor 22 that detects a flow rate of the intakeair, and an intake air temperature sensor 23 that detects a temperatureof the intake air. The housing 21 is made of, for example, a resinmaterial. The flow rate sensor 22 is accommodated in the housing 21. Thehousing 21 of the air flow meter 20 is attached to the intake pipe 14 asuch that the flow rate sensor 22 can come in contact with the intakeair flowing through the intake passage 12.

The housing 21 is attached to the piping unit 14 as an attachmentobject. An outer surface of the housing 21 includes a pair of endsurfaces 21 a and 21 b opposite in the height direction Y. One of thepair of end surfaces 21 a and 21 b included in the inward portion 20 ais referred to as a housing distal end surface 21 a, and anotherincluded in the outward portion 20 b is referred to as a housing basalend surface 21 b. The housing distal end surface 21 a and the housingbasal end surface 21 b are orthogonal to the height direction Y. An endsurface of the pipe flange 14 c is also orthogonal to the heightdirection Y. The attachment object to which the air flow meter 20 andthe housing 21 are attached may not be the piping unit 14 as long as theattachment object is a forming member that forms the intake passage 12.

A surface of the outer surface of the housing 21 facing upstream in theintake passage 12 is referred to as a housing upstream surface 21 c, anda surface of the outer surface of the housing 21 opposite the housingupstream surface 21 c is referred to as a housing downstream surface 21d. In addition, one of a pair of opposite surfaces of the housing 21opposite each other along the housing upstream surface 21 c and thehousing basal end surface 21 b is referred to as a housing front surface21 e, and the other is referred to as a housing back surface 21 f. Thehousing front surface 21 e and a surface of a sensor SA 50 on which theflow rate sensor 22 is provided face in the same direction.

Regarding the housing 21, a direction in which the housing distal endsurface 21 a faces in the height direction Y may be referred to as ahousing distal end direction, and a direction in which the housing basalend surface 21 b faces in the height direction Y may be referred to as ahousing basal end direction. Further, a direction in which the housingupstream surface 21 c faces in the depth direction Z may be referred toas a housing upstream direction, and a direction in which the housingdownstream surface 21 d faces in the depth direction Z may be referredto as a housing downstream direction. Further, a direction in which thehousing front surface 21 e faces in the width direction X may bereferred to as a housing front direction, and a direction in which thehousing back surface 21 f faces in the width direction X may be referredto as a housing back direction.

As shown in FIGS. 2 to 7, the housing 21 includes a seal holder 25, aflange 27 and a connector 28. The air flow meter 20 includes a sealmember 26, and the seal member 26 is attached to the seal holder 25.

The seal holder 25 is provided inside the pipe flange 14 c and holds theseal member 26 so as not to be displaced in the height direction Y. Theseal holder 25 is included in the inward portion 20 a of the air flowmeter 20. The seal holder 25 includes a holding groove 25 a that holdsthe seal member 26. The holding groove 25 a extends in the directions Xand Z orthogonal to the height direction Y. The holding groove 25 amakes a loop around the housing 21. The seal member 26 is a member suchas an O-ring that is inside the pipe flange 14 c and seals the intakepassage 12. The seal member 26 is in a state of being inserted into theholding groove 25 a, and is in tight contact with both an inner surfaceof the holding groove 25 a and an inner peripheral surface of the pipeflange 14 c. Both a portion where the seal member 26 and the innersurface of the holding groove 25 a are in tight contact with each otherand a portion where the seal member 26 and the inner peripheral surfaceof the pipe flange 14 c are in tight contact with each other make a looparound the housing 21.

The flange 27 has a fixing hole such as a screw hole for fixing a fixingtool such as a screw. The fixing tool is used for fixing the housing 21to the intake pipe 14 a. In the present embodiment, the fixing hole is,for example, flange holes 611 and 612, and the fixing tool is screws.Note that, in FIG. 3, the screws inserted in the flange holes 611 and612 are omitted.

A surface of the flange 27 facing in the housing distal end direction isoverlapped and in contact with an end surface of the pipe boss 14 d, andthis overlapped portion is referred to as an angle setting surface 27 a.Both the angle setting surface 27 a and the end surface of the pipe boss14 d extend in a direction orthogonal to the height direction Y, andextend in the width direction X and the depth direction Z. The endsurface of the pipe boss 14 d sets the position and angle of the anglesetting surface 27 a relative to the intake pipe 14 a. The angle settingsurface 27 a sets the position and angle of the housing 21 relative tothe intake pipe 14 a in the air flow meter 20.

In the intake pipe 14 a of the piping unit 14, a main flow of airflowing through the intake passage 12 is along the depth direction Z. Adirection of the main flow is called a main flow direction, and thedepth direction Z coincides with the main flow direction. In the housing21, the angle setting surface 27 a of the flange 27 extends in the mainflow direction and the depth direction Z. The end surface of the pipeboss 14 d also extends in the main flow direction and the depthdirection Z.

The connector 28 is a protection portion for protecting a connectorterminal 28 a electrically connected to the flow rate sensor 22. Theconnector terminal 28 a is electrically connected to the ECU 15. Morespecifically, an electrical wiring extending from the ECU 15 isconnected to the connector 28 via a plug. The flange 27 and theconnector 28 are included in the outward portion 20 b of the air flowmeter 20.

As shown in FIGS. 2, 4, 7, the intake air temperature sensor 23 isprovided outside the housing 21. The intake air temperature sensor 23 isa temperature sensitive element that senses the temperature of intakeair. The intake air temperature sensor 23 is provided on the housingback surface 21 f. The intake air temperature sensor 23 is connected toa lead wire 23 a formed by wiring or the like. The housing 21 includesan intake air temperature support 618. The intake air temperaturesupport 618 is a protrusion provided on the housing back surface 21 f.The intake air temperature support 618 protrudes from the intake airtemperature sensor 23 in the housing back direction along the widthdirection X. The intake air temperature support 618 supports the intakeair temperature sensor 23 by supporting the lead wire 23 a. The intakeair temperature support 618 is provided at a position shifted from theintake air temperature sensor 23 in the housing basal end directionalong the height direction Y. The lead wire 23 a extends from the intakeair temperature support 618 in the housing distal end direction.

The lead wire 23 a extends through the intake air temperature support618 in the height direction Y. At the time of manufacturing of the airflow meter 20, a through hole is formed in the intake air temperaturesupport 618 so as to penetrate through the intake air temperaturesupport 618 in the height direction Y. Then, while the lead wire 23 ainserted through this through hole, the intake air temperature support618 is crushed in the width direction X to crush the through hole.Accordingly, the lead wire 23 a inserted through the through hole isembedded in the intake air temperature support 618. In this case, an endsurface of the intake air temperature support 618 is crushed while beingheated by a heating tool such as a heater such that the intake airtemperature support 618 is thermally deformed. The thermally deformedportion of the intake air temperature support 618 covers and holds thelead wire 23 a. This work can also be called thermal crimping.

As shown in FIG. 8, the housing 21 includes a bypass flow path 30. Thebypass flow path 30 is provided inside the housing 21. The bypass flowpath 30 includes at least a part of an internal space of the housing 21.An inner surface of the housing 21 is a forming surface and forms thebypass flow path 30.

The bypass flow path 30 is disposed in the inward portion 20 a of theair flow meter 20. The bypass flow path 30 includes a through flow path31 and a measurement flow path 32. The flow rate sensor 22 and itssurrounding portions of the sensor SA 50, which will be described later,are in the measurement flow path 32. The through flow path 31 is formedby the inner surface of the housing 21. The measurement flow path 32 isformed by the inner surface of the housing 21 and the outer surface of apart of the sensor SA 50. The intake passage 12 may be referred to as amain passage, and the bypass flow path 30 may be referred to as asub-passage.

The through flow path 31 penetrates through the housing 21 in the depthdirection Z. The through flow path 31 includes a through inlet 33 thatis an upstream end part of the through flow path 31, and a throughoutlet 34 that is a downstream end part of the through flow path 31. Themeasurement flow path 32 is a branch flow path branched from anintermediate part of the through flow path 31. The flow rate sensor 22is provided in the measurement flow path 32. The measurement flow path32 has a measurement inlet 35 which is an upstream end part of themeasurement flow path 32, and a measurement outlet 36 which is adownstream end part of the measurement flow path 32. A boundary betweenthe through flow path 31 and the measurement flow path 32 is a portionwhere the measurement flow path 32 branches from the through flow path31. The measurement inlet 35 is included in the boundary. The boundarybetween the through flow path 31 and the measurement flow path 32 mayalso be referred to as a flow path boundary. The measurement inlet 35faces in the housing distal end direction while being inclined so as toface toward the measurement outlet 36.

The measurement flow path 32 extends from the through flow path 31 inthe housing basal end direction. The measurement flow path 32 isprovided between the through flow path 31 and the housing basal endsurface 21 b. The measurement flow path 32 is curved so that a portionbetween the measurement inlet 35 and the measurement outlet 36 bulges inthe housing basal end direction. The measurement flow path 32 includesan arched portion that curves continuously, a bent portion that bends ina stepwise manner, and a portion that extends straight in the heightdirection Y or the depth direction Z.

The flow rate sensor 22 is a thermal flow rate detection unit having aheater. The flow rate sensor 22 outputs a detection signal according toa temperature change caused by heat generation of the heater. The flowrate sensor 22 is a rectangular parallelepiped chip component, and theflow rate sensor 22 may also be referred to as a sensor chip. The flowrate sensor 22 may also be referred to as a physical quantity sensor ora physical quantity detection unit that detects a flow rate of intakeair as a physical quantity of a fluid.

The air flow meter 20 has a sensor sub-assembly including the flow ratesensor 22, and the sensor sub-assembly is referred to as the sensor SA50. The sensor SA 50 is embedded in the housing 21 while a part of thesensor SA 50 extending into the measurement flow path 32. In the airflow meter 20, the sensor SA 50 and the bypass flow path 30 are arrangedin the height direction Y. More specifically, the sensor SA 50 and thethrough flow path 31 are arranged in the height direction Y. The sensorSA 50 corresponds to a detection unit. The sensor SA 50 may also bereferred to as a measurement unit or a sensor package.

<Description of Configuration Group A>

As shown in FIGS. 9, 10 and 11, the sensor SA 50 includes a sensorsupport 51 in addition to the flow rate sensor 22. The sensor support 51is attached to the housing 21 and supports the flow rate sensor 22. Thesensor support 51 includes an SA substrate 53 and a molded portion 55.The SA substrate 53 is a substrate on which the flow rate sensor 22 ismounted. The molded portion 55 covers at least a part of the flow ratesensor 22 and at least a part of the SA substrate 53. The SA substrate53 may also be called a lead frame.

The molded portion 55 is formed in a plate shape as a whole. An outersurface of the molded portion 55 includes a pair of end surfaces 55 aand 55 b opposite in the height direction Y. One of the pair of endsurfaces 55 a and 55 b facing in the housing distal end direction isreferred to as a molded distal end surface 55 a, and the other facing inthe housing basal end direction is referred to as a molded basal endsurface 55 b. The molded distal end surface 55 a is an end part of themolded portion 55 and an end part of the sensor support 51, andcorresponds to a support end. The molded portion 55 corresponds to aprotective resin.

The outer surface of the molded portion 55 includes a pair of surfaces55 c, 55 d facing each other across the molded distal end surface 55 aand the molded basal end surface 55 b. One of the pair of surfaces 55 c,55 d is referred to as a molded upstream surface 55 c, and the other isreferred to as a molded downstream surface 55 d. In FIG. 8, the sensorSA 50 is arranged inside the housing 21. The molded distal end surface55 a faces in a direction toward a tip end of the air flow meter 20. Themolded upstream surface 55 c is arranged upstream of the moldeddownstream surface 55 d in the measurement flow path 32. In the sensorsupport 51, the molded upstream surface 55 c corresponds to an upstreamend portion, and a molded downstream surface 55 d corresponds to adownstream end portion.

The molded upstream surface 55 c of the sensor SA 50 is arrangedupstream of the molded downstream surface 55 d in the measurement flowpath 32. A flow direction of air in a part of the measurement flow path32 where the flow rate sensor 22 is disposed is opposite to a flowdirection of air in the intake passage 12. Therefore, the moldedupstream surface 55 c is arranged downstream of the molded downstreamsurface 55 d in the intake passage 12. The air flowing along the flowrate sensor 22 flows in the depth direction Z, and this depth directionZ may also be referred to as a flow direction.

As shown in FIGS. 9 and 10, in the sensor SA 50, the flow rate sensor 22is exposed on one side of the sensor SA 50. The outer surface of themold molded portion 55 includes a plate surface referred to as a moldedfront surface 55 e on the same side as the flow rate sensor 22 beingexposed, and a plate surface referred to as a molded back surface 55 fopposite the molded front surface 55 e. One of the plate surfaces of thesensor SA 50 is formed by the molded front surface 55 e. The moldedfront surface 55 e corresponds to a support front surface, and themolded back surface 55 f corresponds to a support back surface.

Regarding the molded portion 55, along the height direction Y, adirection in which the molded distal end surface 55 a faces may bereferred to as a molding direction, and a direction in which the moldedbasal end surface 55 b faces may be referred to as a molding basal enddirection. Along the depth direction Z, a direction in which the moldedupstream surface 55 c faces may be referred to as the molded upstreamdirection, and a direction in which the molded downstream surface 55 dfaces may be referred to as the molded downstream direction. Further,along the width direction X, a direction in which the molded frontsurface 55 e faces may be referred to as a molded frontward direction,and a direction in which the molded back surface 55 f faces may bereferred to as a molded backward direction.

The SA substrate 53 is formed of a metal material or the like in a plateshape as a whole, and is a conductive substrate. A plate surface of theSA substrate 53 is orthogonal to the width direction X and extends inthe height direction Y and the depth direction Z. The flow rate sensor22 is mounted on the SA substrate 53. The SA substrate 53 includes alead terminal 53 a, an upstream test terminal 53 b, and a downstreamtest terminal 53 c. The SA substrate 53 has a part covered by the moldedportion 55 and a part not covered by the molded portion 55, and the partnot covered forms the terminals 53 a, 53 b, 53 c. In FIG. 8 and otherdrawings, the terminals 53 a, 53 b, 53 c are omitted.

The lead terminal 53 a projects in the height direction Y from themolded basal end surface 55 b. Multiple lead terminals 53 a areprovided. The lead terminals 53 a include a terminal connected to theconnector terminal 28 a, a terminal connected to the intake airtemperature sensor 23, and an adjustment terminal for adjusting adetection accuracy of the flow rate sensor 22. In the presentembodiment, the sensor SA 50 has six lead terminals 53 a. These six leadterminals 53 a include three terminals connected to the connectorterminal 28 a, two terminals connected to the intake air temperaturesensor 23, and one adjustment terminal. The three terminals connected tothe connector terminal 28 a include a ground terminal connected to aground, a power supply terminal to which a predetermined voltage such as5V is applied, and an output terminal that outputs a signal related to adetection result of the flow rate sensor 22. The two terminals connectedto the intake air temperature sensor 23 include a ground terminalconnected to the ground, and an output terminal that outputs a signalrelated to a detection result of the intake air temperature sensor 23.

The upstream test terminal 53 b projects in the depth direction Z fromthe molded upstream surface 55 c. Multiple upstream test terminals 53 bare provided. The upstream test terminals 53 b include a capacitor checkterminal for confirming an operation of a capacitor mounted on the SAsubstrate 53, an IC test terminal for confirming an operation of theflow rate sensor 22, and a ground terminal for grounding.

The downstream test terminal 53 c projects in the depth direction Z fromthe molded downstream surface 55 d. Multiple downstream test terminals53 c are provided. Similar to the upstream test terminals 53 b, thedownstream test terminals 53 c include a capacitor check terminal, an ICtest terminal and a ground terminal.

As shown in FIG. 12, the flow rate sensor 22 is formed in a plate shapeas a whole. The flow rate sensor 22 has a sensor front surface 22 a asone surface, and a sensor back surface 22 b opposite the sensor frontsurface 22 a. In the flow rate sensor 22, the sensor back surface 22 bfaces the SA substrate 53, and a part of the sensor front surface 22 ais exposed to an outside of the sensor SA 50.

The flow rate sensor 22 includes a sensor recess portion 61 and amembrane portion 62. The sensor recess portion 61 is provided on thesensor back surface 22 b, and the membrane portion 62 is provided on thesensor front surface 22 a. The membrane portion 62 forms a sensor recessbottom surface 501 that is a bottom surface of the sensor recess portion61. The part of the membrane portion 62 that forms the sensor recessbottom surface 501 is a bottom of the sensor recess portion 61. Thesensor recess portion 61 is formed by the sensor back surface 22 b beingrecessed toward the sensor front surface 22 a. A sensor recess opening503 that is an opening of the sensor recess portion 61 is provided onthe sensor back surface 22 b. A sensor recess inner wall surface 502which is an inner wall surface of the sensor recess portion 61 connectsthe sensor recess bottom surface 501 and the sensor recess opening 503.The membrane portion 62 is a sensing portion that senses a flow rate.

The flow rate sensor 22 includes a sensor substrate 65 and a sensor film66. The sensor substrate 65 is a base material of the flow rate sensor22 and is formed in a plate shape from a semiconductor material such assilicon. The sensor substrate 65 includes a sensor substrate frontsurface 65 a as one surface, and a sensor substrate back surface 65 bopposite the sensor substrate front surface 65 a. The sensor substrate65 has a through hole penetrating through the sensor substrate 65 in thewidth direction X. The sensor recess portion 61 is formed by thisthrough hole. The sensor substrate 65 may have a recess that forms thesensor recess portion 61 instead of the through hole. In this case, thebottom surface of the sensor recess portion 61 is not formed by themembrane portion 62 but by a bottom surface of the recess of the sensorsubstrate 65.

The sensor film 66 is overlaid on the sensor substrate front surface 65a of the sensor substrate 65 and extends in a film shape along thesensor substrate front surface 65 a. In the flow rate sensor 22, thesensor front surface 22 a is formed by the sensor film 66, and thesensor back surface 22 b is formed by the sensor substrate 65. In thiscase, the sensor back surface 22 b is the sensor substrate back surface65 b of the sensor substrate 65.

The sensor film 66 has a multilayer structure including multiple layerssuch as an insulating layer, a conductive layer, and a protective layer.Each of these is formed in a film shape and extends along the sensorsubstrate front surface 65 a. The sensor film 66 has a wiring patternsuch as wiring and resistors, and this wiring pattern is formed by aconductive layer.

In the flow rate sensor 22, the sensor recess portion 61 is formed byprocessing a part of the sensor substrate 65 by wet etching. In themanufacturing process of the flow rate sensor 22, a mask such as asilicon nitride film is attached to the sensor substrate back surface 65b of the sensor substrate 65, and anisotropic etching is performed onthe sensor substrate back surface 65 b using an etching solution untilthe sensor film 66 is exposed. The sensor recess portion 61 may beformed by performing dry etching on the sensor substrate 65.

The sensor SA 50 has a flow rate detection circuit that detects a flowrate of air. At least a part of this flow rate detection circuit isincluded in the flow rate sensor 22. As shown in FIG. 13, the sensor SA50 includes a heating resistor 71, temperature measuring resistors 72,73, and an indirectly heated resistor 74 as circuit elements included inthe flow rate detection circuit. These resistors 71 to 74 are includedin the flow rate sensor 22 and are formed by the conductive layer of thesensor film 66. In this case, the sensor film 66 includes the resistors71 to 74, and these resistors 71 to 74 are included in the wiringpattern of the conductive layer. The resistors 71 to 74 correspond todetection elements. In FIG. 13, the wiring pattern including theresistors 71 to 74 is illustrated by dot hatching. The flow ratedetection circuit may also be referred to as a flow rate measurementunit that measures the flow rate of air.

The heating resistor 71 is a resistance element that generates heataccording to energization of the heating resistor 71. The heatingresistor 71 generates heat to heat the sensor film 66, and correspondsto a heater. The temperature measuring resistors 72, 73 are resistanceelements for detecting a temperature of the sensor film 66, andcorrespond to a temperature detector. The resistance values of thetemperature measuring resistors 72, 73 change according to thetemperature of the sensor film 66. In the flow rate detection circuit,the temperature of the sensor film 66 is detected using the resistancevalues of the temperature measuring resistors 72, 73. The flow ratedetection circuit raises the temperature of the sensor film 66 and thetemperatures of the temperature measuring resistors 72 and 73 by theheating resistor 71. When an air flow occurs in the measurement flowpath 32, the flow rate detection circuit detects an air flow rate and aflow direction by using change in temperature detected by thetemperature measuring resistors 72, 73.

The heating resistor 71 is arranged substantially at the center of themembrane portion 62 in each of the height direction Y and the depthdirection Z. The heating resistor 71 is formed in a rectangular shapeextending in the height direction Y as a whole. The center line CL1 ofthe heating resistor 71 passes through the center CO1 of the heatingresistor 71 and extends linearly in the height direction Y. The centerline CL1 passes through the center of the membrane portion 62. Theheating resistor 71 is arranged at a position spaced inward from aperipheral edge of the membrane portion 62. An end of the heatingresistor 71 facing in a molding distal end direction and an end of theheating resistor 71 facing in a molding basal end direction are the samein distance from the center CO1.

Each of the temperature measuring resistors 72, 73 is formed in arectangular shape extending in the height direction Y as a whole. Thetemperature measuring resistors 72, 73 are arranged in the depthdirection Z. The heating resistor 71 is disposed between the temperaturemeasuring resistors 72, 73. An upstream temperature measuring resistor72 among the temperature measuring resistors 72, 73 is provided at aposition separated from the heating resistor 71 in a molded upstreamdirection. A downstream temperature measuring resistor 73 among thetemperature measuring resistors 72, 73 is provided at a positionseparated from the heating resistor 71 in a molded downstream direction.The center line CL2 of the upstream temperature measuring resistor 72and the center line CL3 of the downstream temperature measuring resistor73 both linearly extend parallel to the center line CL1 of the heatingresistor 71. The heating resistor 71 is disposed at an intermediateposition between the upstream temperature measuring resistor 72 and thedownstream temperature measuring resistor 73 in the depth direction Z.

Regarding the sensor SA 50 of the present embodiment, in FIG. 10, adirection in which the molded upstream surface 55 c faces is referred toas the molded upstream direction, and a direction in which the moldeddownstream surface 55 d faces is referred to as the molded downstreamdirection. Further, a direction in which the molded distal end surface55 a faces is referred to as the molding distal end direction, and adirection in which the molded basal end surface 55 b faces is referredto as the molding basal end direction.

Returning to the explanation of FIG. 13, the indirectly heated resistor74 is a resistance element for detecting a temperature of the heatingresistor 71. The indirectly heated resistor 74 extends along theperipheral edge of the heating resistor 71. A resistance value of theindirectly heated resistor 74 changes according to the temperature ofthe heating resistor 71. In the flow rate detection circuit, thetemperature of the heating resistor 71 is detected using the resistancevalue of the indirectly heated resistor 74.

The sensor SA 50 includes a heating wire 75 and temperature measuringwires 76. 77. These wires 75 to 77 are included in the wiring pattern ofthe sensor film 66, like the resistors 71 to 74. The heating wire 75extends from the heating resistor 71 in the molding basal end directionalong the height direction Y. The upstream temperature measuring wire 76extends from the upstream temperature measuring resistor 72 in themolding distal end direction along the height direction Y. Thedownstream temperature measuring wire 77 extends from the downstreamtemperature measuring resistor 73 in the molding distal end directionalong the height direction Y.

As shown in FIGS. 14 and 15, a center line CL4 of the measurement flowpath 32 passes through a center CO2 of the measurement inlet 35 and acenter CO3 of the measurement outlet 36, and extends linearly along themeasurement flow path 32. The sensor SA 50 is provided in themeasurement flow path 32 between the measurement inlet 35 and themeasurement outlet 36. The sensor SA 50 is disposed at a positiondownstream away from the measurement inlet 35 and upstream away from themeasurement outlet 36. In FIG. 14, a center line of a region of themeasurement flow path 32 excluding an internal space of a SA insertionhole 107 is shown as the center line CL4.

In the through flow path 31, an opening area of the through outlet 34 issmaller than the opening area of the through inlet 33. A height of thethrough outlet 34 and a height of the through inlet 33 are the same inthe height direction Y while a width of the through outlet 34 is smallerthan a width of the through inlet 33 in the width direction X. Theopening area of the through inlet 33 is an area of a region including acenter CO21 of the through inlet 33. The opening area of the throughoutlet 34 is an area of a region including a center CO24 of the throughoutlet 34.

In the measurement flow path 32, a total value of respective openingareas of multiple measurement outlets 36 is smaller than an opening areaof the measurement inlet 35. This may be simply said that the openingarea of the measurement outlet 36 is smaller than the opening area ofthe measurement inlet 35. The opening area of the measurement inlet 35is an area of a region including a center CO2 of the measurement inlet35. The opening area of the measurement outlet 36 is an area of a regionincluding a center CO3 of the measurement outlet 36.

As shown in FIGS. 15, 16, the housing 21 includes a measurement floorsurface 101, a measurement ceiling surface 102, a front measurement wallsurface 103, and a back measurement wall surface 104 as formationsurfaces forming the measurement flow path 32. The measurement floorsurface 101, the measurement ceiling surface 102, the front measurementwall surface 103, and the back measurement wall surface 104 all extendalong the center line CL4 of the measurement flow path 32. Themeasurement floor surface 101, the measurement ceiling surface 102, thefront measurement wall surface 103, and the back measurement wallsurface 104 form a part of the measurement flow path 32 extending in thedepth direction Z. The measurement floor surface 101 corresponds to afloor surface, the front measurement wall surface 103 corresponds to afront wall surface, and the back measurement wall surface 104corresponds to a back wall surface. The width direction X corresponds toa front-back direction in which the front wall surface and the back wallsurface faces each other.

The measurement floor surface 101 and the measurement ceiling surface102 are provided between the front measurement wall surface 103 and theback measurement wall surface 104. The measurement floor surface 101faces the molded distal end surface 55 a of the sensor SA 50 and extendsstraight in the depth direction Z. The measurement ceiling surface 102is opposite and facing to the measurement floor surface 101 across thecenter line CL4 in the height direction Y. The SA insertion hole 107 isprovided in a portion of the housing 21 that forms the measurementceiling surface 102, and the sensor SA 50 is inserted into the SAinsertion hole 107. The SA insertion hole 107 is closed by the sensor SA50. The measurement flow path 32 also includes a gap between the sensorSA 50 and the housing 21 in the internal space of the SA insertion hole107.

The front measurement wall surface 103 and the back measurement wallsurface 104 are a pair of wall surfaces facing each other across themeasurement floor surface 101 and the measurement ceiling surface 102.The front measurement wall surface 103 faces the molded front surface 55e of the sensor SA 50, and extends in the housing basal end directionfrom an edge of the measurement floor surface 101 on an airflow-meterfront side. The front measurement wall surface 103 faces the flow ratesensor 22 of the sensor SA 50. The back measurement wall surface 104faces the molded back surface 55 f of the sensor SA 50, and extends inthe housing basal end direction from an edge of the measurement floorsurface 101 on an airflow-meter back side. In FIGS. 15, 16, the internalstructure of the sensor SA 50 is simplified and only the molded portion55 and the flow rate sensor 22 are shown.

The housing 21 has a front narrowed portion 111 and a back narrowedportion 112. These narrowed portions 111, 112 gradually narrow themeasurement flow path 32 such that a cross-sectional area S4 of themeasurement flow path 32 gradually decreases from an upstream part suchas the measurement inlet 35 in a direction toward the flow rate sensor22. Further, the narrowed portions 111, 112 gradually narrow themeasurement flow path 32 such that the cross-sectional area S4 of themeasurement flow path 32 gradually decreases from a downstream part suchas the measurement outlet 36 in a direction toward the flow rate sensor22. Regarding the measurement flow path 32, an area orthogonal to thecenter line CL4 is referred to as the cross-sectional area S4, and thiscross-sectional area S4 may also be referred to as a flow path area.

The front narrowed portion 111 is a convex portion in which a part ofthe front measurement wall surface 103 protrudes toward the backmeasurement wall surface 104. The back narrowed portion 112 is a convexportion in which a part of the back measurement wall surface 104protrudes toward the front measurement wall surface 103. The frontnarrowed portion 111 and the back narrowed portion 112 are arrangedalong the height direction Y and face each other in the width directionX. These narrowed portions 111, 112 are bridged by the measurementceiling surface 102 and the measurement floor surface 101. The narrowedportions 111, 112 gradually reduce a measurement width dimension W1 in adirection from upstream to the flow rate sensor 22. The measurementwidth dimension W1 is a distance in the width direction X between thefront measurement wall surface 103 and the back measurement wall surface104. Further, the narrowed portions 111, 112 gradually reduce themeasurement width dimension W1 in a direction from downstream to theflow rate sensor 22.

The narrowed portions 111, 112 gradually approach the center line CL4 inthe direction from upstream to the flow rate sensor 22 in themeasurement flow path 32. In the measurement flow path 32, the distancesW2, W3 in the width direction X between the narrowed portions 111, 112and the center line CL4 gradually decrease in the direction fromupstream to the flow rate sensor 22. The narrowed portions 111, 112gradually approach the center line CL4 in the direction from downstreamto the flow rate sensor 22 in the measurement flow path 32. In themeasurement flow path 32, the distances W2, W3 in the width direction Xbetween the narrowed portions 111, 112 and the center line CL4 graduallydecrease in the direction from downstream to the flow rate sensor 22.

In the narrowed portions 111, 112, the parts closest to the center lineCL4 are peaks 111 a, 112 a. In this case, in the narrowed portions 111,112, the distances W2, W3 from the center line CL4 are smallest at thepeaks 111 a, 112 a. The peaks 111 a, 112 a are a front peak 111 a of thefront narrowed portion 111 and a back peak 112 a of the back narrowedportion 112. The front peak 111 a and the back peak 112 a are arrangedin the width direction X and face each other.

The flow rate sensor 22 is disposed between the front narrowed portion111 and the back narrowed portion 112. More specifically, the center CO1of the heating resistor 71 of the flow rate sensor 22 is providedbetween the front peak 111 a and the back peak 112 a. Regarding theheating resistor 71, a center line CL5 is defined as a straightimaginary line that passes through the center CO1, is orthogonal to thecenter line CL1 and extends in the width direction X. Both the frontpeak 111 a and the back peak 112 a are located on the center line CL5.In this case, the center CO1 of the heating resistor 71 and the frontpeak 111 a are aligned in the width direction X. The center CO1 of theheating resistor 71 and the front peak 111 a face each other in thewidth direction X.

As shown in FIG. 16, the sensor support 51 of the sensor SA 50 isprovided at a position closer to the front narrowed portion 111 than tothe back narrowed portion 112 in the width direction X. That is, thesensor support 51 is provided at a position closer to the frontmeasurement wall surface 103 than to the back measurement wall surface104. On the center line CL5 of the heating resistor 71, a front distanceL1 that is a distance in the width direction X between the flow ratesensor 22 and the front measurement wall surface 103 is smaller than aback distance L2 that is a distance in the width direction X between theflow rate sensor 22 and the back measurement wall surface 104. That is,there is a relationship of L1<L2. The front distance L1 is a distancebetween the center CO1 of the heating resistor 71 and the front peak 111a of the front narrowed portion 111. The back distance L2 is a distanceon the center line CL5 of the heating resistor 71 between the moldedback surface 55 f and the back peak 112 a of the back narrowed portion112.

The molded distal end surface 55 a of the sensor support 51 is arrangedat a position closer to the measurement floor surface 101 than to themeasurement ceiling surface 102 in the height direction Y. In this case,in the measurement flow path 32, a floor distance L3 is smaller than thefront distance L1. That is, there is a relationship of L1>L3. The floordistance L3 is a distance between the molded distal end surface 55 a andthe measurement floor surface 101 in the height direction Y. Morespecifically, the floor distance L3 is a distance between the moldeddistal end surface 55 a and a portion of the measurement floor surface101 that is closest to the molded distal end surface 55 a within aregion of the measurement floor surface 101 facing the molded distal endsurface 55 a.

In the measurement flow path 32, a sensor region 121 is defined as aplanar region that is defined by the inner surface of the housing 21 andan outer surface of the sensor SA 50, is orthogonal to the center lineCL4 and passes through the center CO1 of the heating resistor 71. Theair flowing from the measurement inlet 35 to the measurement outlet 36in the measurement flow path 32 needs to pass through the sensor region121.

The sensor region 121 includes a front region 122 and a back region 123.The front region 122 is between the front measurement wall surface 103and the molded front surface 55 e in the width direction X. The backregion 123 is between the back measurement wall surface 104 and themolded back surface 55 f in the width direction X. These regions 122 and123 extend in the height direction Y from the measurement floor surface101 toward the measurement ceiling surface 102. In the measurement flowpath 32, the sensor SA 50 is arranged between the front region 122 andthe back region 123 in the width direction X.

The front region 122 includes a floor region 122 a and a ceiling region122 b. The floor region 122 a is a region in the front region 122 thatextends from a floor-directed end of the flow rate sensor 22 toward themeasurement floor surface 101. An edge of the floor region 122 a facingin the housing distal end direction is defined by the measurement floorsurface 101. Therefore, the floor region 122 a is between the flow ratesensor 22 and the measurement floor surface 101 in the height directionY. The ceiling region 122 b is a region in the front region 122 thatextends from a ceiling-directed end of the flow rate sensor 22 towardthe measurement ceiling surface 102. An edge of the front region 122facing in the housing basal end direction is defined by a ceilingboundary which is a boundary between the inner surface of the housing 21and the outer surface of the sensor SA 50. Therefore, the ceiling region122 b is between the flow rate sensor 22 and the ceiling boundary in theheight direction Y.

An area of the sensor region 121 is defined as a region area S1, and theregion area S1 is a cross-sectional area of a portion of the measurementflow path 32 where the flow rate sensor 22 is provided. The region areaS1 includes a floor area S2 which is an area of the floor region 122 a,and a ceiling area S3 which is an area of the ceiling region 122 b. Inthe front region 122, the ceiling area S3 is smaller than the floor areaS2. That is, there is a relationship of S3<S2.

According to the present embodiment described thus far, the frontdistance L1 is larger than the floor distance L3 in the measurement flowpath 32. According this configuration, an amount of air flowing alongthe front measurement wall surface 103 or the molded front surface 55 eis likely to be larger than an amount of air flowing along themeasurement floor surface 101 or the molded distal end surface 55 a. Inthis case, since air easily flows along the flow rate sensor 22 on themolded front surface 55 e, decrease in flow rate detection accuracy ofthe flow rate sensor 22 caused by shortage of an amount of air flowingalong the flow rate sensor 22 is unlikely to occur. Therefore, the flowrate detection accuracy of the flow rate sensor 22 can be increased, andas a result, the air flow rate measurement accuracy of the air flowmeter 20 can be increased.

In the configuration in which the floor distance L3 is smaller than thefront distance L1, the measurement flow path 32 may be narrowed from themeasurement floor surface 101 and the region area S1 of the sensorregion 121 may become insufficient. In the measurement flow path 32, ifthe cross-sectional area such as the region area S1 becomesinsufficient, a pressure loss increases, and air becomes difficult toflow from the through flow path 31 into the measurement flow path 32. Inthis case, an air flow rate in the measurement flow path 32 may becomeinsufficient, and separation or turbulence of air flow may easily occurin the measurement flow path 32. As a result, the detection result ofthe flow rate sensor 22 is likely to include noise due to the separationor turbulence.

With respect to this, according to the present embodiment, the frontdistance L1 is smaller than the back distance L2 in the measurement flowpath 32. In this case, even if the area between the molded distal endsurface 55 a of the sensor SA 50 and the measurement floor surface 101is narrow, the back region 123 between the molded back surface 55 f andthe back measurement wall surface 104 is relatively wide. According tothis configuration, the shortage of the region area S1 of the sensorregion 121 can be avoided by the back region 123, and the shortage ofthe air flow rate in the measurement flow path 32 is less likely tooccur. In this case, separation and turbulence of air flow is lesslikely to occur in the measurement flow path 32, and noise contaminationin the detection result of the flow rate sensor 22 can be reduced.Further, in this case, since the pressure loss in the measurement flowpath 32 is reduced and the flow rate is likely to be increased, a rangeof flow rate detection by the flow rate sensor 22 can be expanded. Thatis, fluctuation of an output from the air flow meter 20 can be reduced,and the air flow meter 20 can have a large dynamic range. Therefore, theair flow meter 20 can realize both reduction in output fluctuation andincrease in dynamic range.

The front distance L1 is smaller than the back distance L2. According tothis configuration, at the time of manufacturing of the air flow meter20, even if a relative position of the sensor SA 50 with respect to thehousing 21 shifts in the width direction X due to an error in attachingthe sensor SA 50 to the housing 21, the front distance L1 can be easilykept smaller than the back distance L2. As described above, even if anerror in attaching the sensor SA 50 to the housing 21 occurs, therelationship between the front distance L1 and the back distance L2 canrealize a configuration in which the detection accuracy of the flow ratesensor 22 is difficult to decrease.

According to this embodiment, the housing 21 includes the front narrowedportion 111. In this configuration, the front narrowed portion 111gradually narrows the measurement flow path 32 in the direction from themeasurement inlet 35 toward the flow rate sensor 22. Thus, even ifseparation or turbulence is generated in the air flow, the frontnarrowed portion 111 reduces the separation and turbulence by regulatingthe air flow. In this case, the separation or turbulence is unlikely toreach the flow rate sensor 22. Thus, the detection accuracy of the flowrate sensor 22 can be improved. Moreover, since the front distance L1 isthe distance between the front narrowed portion 111 and the flow ratesensor 22, air flowing along the flow rate sensor 22 can be reliablyregulated by the front narrowed portion 111.

According to the present embodiment, the front distance L1 is thedistance between the front peak 111 a of the front narrowed portion 111and the flow rate sensor 22. In the front narrowed portion 111, aportion having the highest regulation effect is likely to be the frontpeak 111 a. Therefore, since the portion having the highest regulationeffect faces the flow rate sensor 22, occurrence of separation andturbulent in the air flow along the flow rate sensor 22 can be reliablyreduced. Accordingly, the detection accuracy of the flow rate sensor 22can be further improved.

According to the present embodiment, the housing 21 includes the backnarrowed portion 112. In this configuration, the back narrowed portion112 gradually narrows the measurement flow path 32 in the direction fromthe measurement inlet 35 toward the flow rate sensor 22. Thus, even ifseparation or turbulence is generated in the air flow, the back narrowedportion 112 reduces the separation and turbulence by regulating the airflow. In the measurement flow path 32, air flowing toward the flow ratesensor 22 at a height position near the flow rate sensor 22 in theheight direction Y is expected to easily pass through both the frontside and the back side of the sensor support 51. Therefore, theregulation of the air flow along the back measurement wall surface 104by the back narrowed portion 112 is effective in preventing theseparation and the turbulence from reaching the flow rate sensor 22.

According to the present embodiment, in the measurement flow path 32,the ceiling area S3 of the ceiling region 122 b is smaller than thefloor area S2 of the floor region 122 a. According to thisconfiguration, the pressure loss is more likely to increase in theceiling region 122 b than in the floor region 122 a, and it is difficultfor air to flow in the ceiling region 122 b. Therefore, even if themeasurement flow path 32 has a configuration in which an air flow alongthe measurement ceiling surface 102 tends to be lager in velocity andvolume than an air flow along the measurement floor surface 101, thevelocity and volume of air flow can be equalized in the ceiling region122 b and the floor region 122 a. As a result, deterioration indetection accuracy of the flow rate sensor 22 due to mixing of the fastand slow airflows reaching the sensor region 121 can be reduced.

According to the present embodiment, the measurement flow path 32 iscurved so that the measurement ceiling surface 102 becomes an outercurve and the measurement floor surface 101 becomes an inner curve.According to this configuration, an air flow along the measurementceiling surface 102 tends to be lager in velocity and volume than theair flow along the measurement floor surface 101 due to centrifugalforce or the like. Therefore, the fact that the ceiling area S3 issmaller than the floor area S2 is effective for equalizing thevelocities and volumes of the air flows in the ceiling region 122 b andthe floor region 122 a.

According to the present embodiment, the front distance L1 is thedistance between the front measurement wall surface 103 and the heatingresistor 71. In the flow rate sensor 22, since a flow rate of airflowing along the heating resistor 71 is detected, the detectionaccuracy of the flow rate sensor 22 can be increased by managing thepositional relationship between the heating resistor 71 and the frontmeasurement wall surface 103.

According to the present embodiment, in the sensor SA 50, the moldedfront surface 55 e and the molded back surface 55 f are both formed bythe resin molded portion 55. In this configuration, smoothness of themolded front surface 55 e and the molded back surface 55 f can be easilymanaged. Thus, separation or turbulence is less likely to be generatedin air flowing along the molded front surface 55 e and the molded backsurface 55 f.

<Description of Configuration Group B>

As shown in FIGS. 8 and 17, the housing 21 includes an SA containerspace 150. The SA container space 150 is provided at a position shiftedfrom the bypass flow path 30 in the housing basal end direction. The SAcontainer space 150 houses a part of the sensor SA 50. At least themolded basal end surface 55 b of the sensor SA 50 is housed in the SAcontainer space 150. The measurement flow path 32 and the SA containerspace 150 are arranged in the height direction Y. The sensor SA 50 ispositioned to extend in the height direction Y across a boundary betweenthe measurement flow path 32 and the SA container space 150. At leastthe molded distal end surface 55 a and the flow rate sensor 22 of thesensor SA 50 are housed in the measurement flow path 32. The SAcontainer space 150 corresponds to a container space. In FIGS. 17, 18,the internal structure of the sensor SA 50 is simplified and only themolded portion 55 and the flow rate sensor 22 are shown.

The housing 21 includes a first housing part 151 and a second housingpart 152. The housing parts 151 and 152 are assembled and integratedwith each other so as to form the housing 21. The first housing part 151forms the SA container space 150. The first housing part 151 forms thebypass flow path 30 in addition to the SA container space 150. An innersurface of the first housing part 151 that is an inner surface of thehousing 21 defines the SA container space 150 and the bypass flow path30. A housing opening 151 a (see FIG. 19) is provided at an open end ofthe first housing part 151. The SA container space 150 is open throughthe housing opening 151 a in a direction away from the measurement flowpath 32.

When the sensor SA 50 is housed in the SA container space 150 and themeasurement flow path 32, a gap is formed between the outer surface ofthe sensor SA 50 and the inner surface of the first housing part 151.The second housing part 152 fills this gap. More specifically, thesecond housing part 152 is inserted between the outer surface of thesensor SA 50 and the inner surface of the first housing part 151 in theSA container space 150.

As shown in FIG. 17, the housing 21 includes a housing partition 131.The housing partition 131 is a protrusion provided on the inner surfaceof the first housing part 151, and projects from the first housing part151 toward the sensor SA 50. In this case, the first housing part 151includes the housing partition 131. A tip end of the housing partition131 is in contact with the outer surface of the sensor SA 50. Thehousing partition 131 is between the outer surface of the sensor SA 50and the inner surface of the first housing part 151 and separates the SAcontainer space 150 from the measurement flow path 32.

The inner surface of the first housing part 151 includes a housing flowpath surface 135, a housing container surface 136, and a housing stepsurface 137. The housing flow path surface 135, the housing containersurface 136, and the housing step surface 137 extend in a directionintersecting the height direction Y. Each of the surfaces 135, 136, 137extends to make a loop around the sensor SA 50. In the sensor SA 50, thecenter line CL1 of the heating resistor 71 extends in the heightdirection Y. The housing flow path surface 135, the housing containersurface 136, and the housing step surface 137 extend in acircumferential direction around the center line CL1.

In the first housing part 151, the housing step surface 137 is providedbetween the housing distal end surface 21 a and the housing basal endsurface 21 b. The housing step surface 137 faces in the housing basalend direction along the height direction Y. The housing step surface 137is inclined with respect to the center line CL1. The housing stepsurface 137 faces inward in a radial direction, i.e. in a directiontoward the center line CL1. The housing step surface 137 intersects theheight direction Y and corresponds to a housing intersecting surface. Onthe inner surface of the first housing part 151, an external cornerbetween the housing flow path surface 135 and the housing step surface137 and an internal corner between the housing container surface 136 andthe housing step surface 137 are chamfered. The height direction Ycorresponds to an arrangement direction in which the measurement flowpath and the container space are arranged.

The housing flow path surface 135 forms the measurement flow path 32.The housing flow path surface 135 extends from an inner peripheral edgeof the housing step surface 137 in the housing distal end direction. Thehousing flow path surface 135 extends from the housing step surface 137in a direction away from the SA container space 150. On the other hand,the housing container surface 136 forms the SA container space 150. Thehousing container surface 136 extends from an outer peripheral edge ofthe housing step surface 137 in the housing basal end direction. Thehousing container surface 136 extends from the housing step surface 137in a direction away from the measurement flow path 32. The housing stepsurface 137 is provided between the housing flow path surface 135 andthe housing container surface 136, and forms a step on the inner surfaceof the first housing part 151. The housing step surface 137 connects thehousing flow path surface 135 and the housing container surface 136.

An outer surface of the molded portion 55 forms the outer surface of thesensor SA 50. The outer surface of the sensor SA 50 includes an SA flowpath surface 145, an SA container surface 146, and an SA step surface147. The SA flow path surface 145, the SA container surface 146, and theSA step surface 147 extend in a direction intersecting the heightdirection Y. Each of the surfaces 145, 146, 147 extends to make a loopon the outer surface of the sensor SA 50. The SA flow path surface 145,the SA container surface 146, and the SA step surface 147 extend in thecircumferential direction around the center line CL1 of the heatingresistor 71.

In the sensor SA 50, the SA step surface 147 is provided between themolded distal end surface 55 a and the molded basal end surface 55 b.The SA step surface 147 faces toward the molded distal end surface 55 ain the height direction Y. The SA step surface 147 is inclined withrespect to the center line CL1. The SA step surface 147 faces outward ina radial direction, i.e. in a direction away from the center line CL1.The SA step surface 147 intersects the height direction Y andcorresponds to a unit intersecting surface. Further, the SA flow pathsurface 145 corresponds to a unit flow path surface, and the SAcontainer surface 146 corresponds to a unit container surface. On theouter surface of the sensor SA 50, an internal corner between the SAflow path surface 145 and the SA step surface 147 and an external cornerbetween the SA container surface 146 and the SA step surface 147 arechamfered.

The SA flow path surface 145 forms the measurement flow path 32. The SAflow path surface 145 extends from an inner peripheral edge of the SAstep surface 147 in the molding distal end direction along the heightdirection Y. The SA flow path surface 145 extends from the SA stepsurface 147 in a direction away from the SA container space 150. On theother hand, the SA container surface 146 forms the SA container space150. The SA container surface 146 extends from an outer peripheral edgeof the SA step surface 147 in the molding basal end direction. The SAcontainer surface 146 extends from the SA step surface 147 in adirection away from the measurement flow path 32. The SA step surface147 is provided between the SA flow path surface 145 and the SAcontainer surface 146, and forms a step on the outer surface of thesensor SA 50. The SA step surface 147 connects the SA flow path surface145 and the SA container surface 146.

In the sensor SA 50, the molded upstream surface 55 c, the moldeddownstream surface 55 d, the molded front surface 55 e, and the moldedback surface 55 f form the SA flow path surface 145, the SA containersurface 146, and the SA step surface 147.

In the air flow meter 20, the housing step surface 137 facing in thehousing basal end direction and the SA step surface 147 facing in thehousing distal end direction face each other. Further, the housing flowpath surface 135 facing radially inward and the SA flow path surface 145facing radially outward face each other. Similarly, the housingcontainer surface 136 facing radially inward and the SA containersurface 146 facing radially outward face each other.

The housing partition 131 is provided on the housing step surface 137and extends in the housing basal end direction along the heightdirection Y. A center line CL11 of the housing partition 131 extendslinearly in the height direction Y. The housing partition 131, togetherwith the housing step surface 137, extends to make a loop around thesensor SA 50. In this case, as shown in FIG. 19, the housing partition131 has a portion extending in the width direction X and a portionextending in the depth direction Z. The housing partition 131 has asubstantially rectangular frame shape as a whole.

Returning to the description of FIG. 17, the tip end of the housingpartition 131 is in contact with the SA step surface 147 of the outersurface of the sensor SA 50. The housing partition 131 and the SA stepsurface 147 are in tight contact with each other, and enhance a sealingproperty of the part that separates the SA container space 150 from themeasurement flow path 32. The SA step surface 147 is flat and extendsstraight in a direction intersecting the height direction Y. In thepresent embodiment, the housing step surface 137 and the SA step surface147 do not extend parallel to each other. The SA step surface 147 isinclined with respect to the housing step surface 137. As describedabove, even if the SA step surface 147 and the housing step surface 137are not parallel to each other, the sealing property is improved at thepart where the outer surface of the sensor SA 50 and the inner surfaceof the first housing part 151 because the housing partition 131 is incontact with the SA step surface 147. The housing step surface 137 andthe SA step surface 147 may extend parallel to each other.

The housing partition 131 is orthogonal to the housing step surface 137.In this case, the center line CL11 of the housing partition 131 and thehousing step surface 137 are orthogonal to each other. The housingpartition 131 has a tapered shape. The directions X, Z orthogonal to theheight direction Y are width directions of the housing partition 131,and widths of the housing partition 131 in the width directionsgradually decreases toward the tip end of the housing partition 131.Each of a pair of lateral surfaces of the housing partition 131 extendsstraight from the housing step surface 137. In this case, the housingpartition 131 has a tapered cross section.

The housing partition 131 is arranged at a position on the housing stepsurface 137 closer to the housing flow path surface 135 than to thehousing container surface 136. In this case, in the directions X, Zorthogonal to the height direction Y, a distance between the housingpartition 131 and the housing container surface 136 is smaller than adistance between the housing partition 131 and the housing flow pathsurface 135.

A portion of the housing step surface 137, which is between the housingflow path surface 135 and the housing partition 131, and the housingflow path surface 135 form the measurement flow path 32. A portion ofthe housing step surface 137, which is between the housing containersurface 136 and the housing partition 131, and the housing containersurface 136 form the SA container space 150.

A portion of the SA step surface 147, which is between the SA flow pathsurface 145 and the housing partition 131, and the SA flow path surface145 form the measurement flow path 32. A portion of the SA step surface147, which is between the SA container surface 146 and the housingpartition 131, and the SA container surface 146 form the SA containerspace 150.

Next, referring to FIGS. 18 to 21, a manufacturing method of the airflow meter 20 will be described focusing on a procedure of mounting thesensor SA 50 to the housing 21.

The manufacturing process of the air flow meter 20 includes a step ofmanufacturing the sensor SA 50 and a step of manufacturing the firsthousing part 151 by, for example, resin molding. After these steps, astep of assembling the sensor SA 50 with the first housing part 151 isperformed.

At the step of manufacturing the sensor SA 50, the molded portion 55 ofthe sensor SA 50 is manufactured by resin molding using an injectionmolding machine or an injection molding device provided with a molddevice. At this step, a molten resin obtained by melting a resinmaterial is injected from an injection molding machine and press-fittedinto the mold device. Further, at this step, an epoxy thermosettingresin such as an epoxy resin is used as the resin material for formingthe molded portion 55.

At the step of manufacturing the first housing part 151, the firsthousing part 151 is manufactured by resin molding or the like using aninjection molding device or the like. At this step, a thermoplasticresin such as polybutylene terephthalate (PBT) or polyphenylene sulfide(PPS) is used as the resin material forming the first housing part 151.The first housing part 151 formed of the thermoplastic resin asdescribed above is softer than the molded portion 55 formed of thethermosetting resin. In other words, the first housing part 151 haslower hardness and higher flexibility than the molded portion 55.

At the step of assembling the sensor SA 50 to the first housing part151, the sensor SA 50 is inserted into the first housing part 151through the housing opening 151 a as shown in FIG. 18. At this step, asshown in FIG. 20, the SA step surface 147 contacts the tip end of thehousing partition 131, and then, the sensor SA 50 is further pushed intothe first housing part 151 in the housing distal end direction. In thiscase, since the hardness of the first housing part 151 is lower than thehardness of the molded portion 55, the tip end of the housing partition131 is deformed via crushing by the SA step surface 147 as shown in FIG.21. The crushing of the tip end of the housing partition 131 newlygenerates a tip end surface which is easily come into tight contact withthe SA step surface 147. Accordingly, the sealing performance betweenthe housing partition 131 and the SA step surface 147 is improved. InFIG. 17, a portion of the housing partition 131 which was crushed by thesensor SA 50 is illustrated by a chain double-dashed line as animaginary line.

At the step of assembly of the sensor SA 50, when the tip end of thehousing partition 131 is crushed by the SA step surface 147, fragmentsof the housing partition 131 may be generated as crushed dust, and thecrushed dust may enter the measurement flow path 32. If the crushed dustthat has entered the measurement flow path 32 comes into contact with oradheres to the flow rate sensor 22 as foreign matter in the measurementflow path 32, the detection accuracy of the flow rate sensor 22 may bereduced.

On the other hand, in the present embodiment, the crushed dust isdifficult to enter the measurement flow path 32. More specifically, asshown in FIG. 20, angles between the center line CL11 of the housingpartition 131 and the SA step surface 147 include a container angle θ12facing the SA container space 150 and a flow path angle θ11 facing themeasurement flow path 32. The container angle θ12 is larger than theflow path angle θ11. That is, there is a relationship of θ12>θ11.According to this configuration, the tip end of the housing partition131 is more likely to tilt or collapse toward the SA container space 150than toward the measurement flow path 32. Therefore, even if the crusheddust is generated, it is difficult for the crushed dust to enter themeasurement flow path 32.

The flow path angle θ11 is an angle at a portion closest to the SA stepsurface 147 in the outer surface of the housing partition 131. Thecontainer angle θ12 is an angle on another side of the center line CL11opposite the flow path angle θ11.

After the sensor SA 50 is attached to the first housing part 151, a stepof manufacturing the second housing part 152 by resin molding or thelike using an injection molding device or the like is performed. At thisstep, the mold device is mounted on the first housing part 151 togetherwith the sensor SA 50, and a molten resin obtained by melting a resinmaterial is injected from an injection molding machine and press-fittedinto the mold device. According to the injection of the molten resininto the mold device, the molten resin is filled in a gap between thefirst housing part 151 and the sensor SA 50. In this case, since thehousing partition 131 is in contact with the outer surface of the sensorSA 50 as described above, the molten resin is prevented from enteringthe measurement flow path 32 through the gap between the first housingpart 151 and the sensor SA 50. Then, the second housing part 152 isformed by solidifying the molten resin inside the mold device.

Similar to the first housing part 151, a thermoplastic resin such aspolybutylene terephthalate (PBT) or polyphenylene sulfide (PPS) is usedas the resin material forming the second housing part 152. Both of thefirst housing part 151 and the second housing part 152 contain a carbonmaterial having conductivity. Examples of the carbon material includecarbon powder, carbon fiber, nanocarbon, graphene, and carbonmicroparticles.

The first housing part 151 is easier to discharge when charged than thesecond housing part 152. For example, the first housing part 151 islarger in content rate and content of the carbon material than thesecond housing part 152. A portion of the housing 21 that easily becomesa path for electric charges during discharging is referred to as aconductive portion. The conductive portion is larger in the firsthousing part 151 than in the second housing part 152. The conductiveportion includes multiple ones of carbon powder, carbon fiber,nanocarbon, graphene and carbon microparticles. Examples of thenanocarbon include carbon nanotube, carbon nanofiber, and fullerene.

According to the present embodiment described above, the housingpartition 131 protruding from the inner surface of the housing 21 isbetween the sensor SA 50 and the housing 21 and separates themeasurement flow path 32 from the SA container space 150. In thisconfiguration, since the tip end of the housing partition 131 and thesensor SA 50 easily come into contact with each other, a gap is unlikelyto be formed between the inner surface of the housing 21 and the outersurface of the sensor SA 50. When the molten resin is injected into theSA container space 150 of the first housing part 151 for forming thesecond housing part 152, the molten resin is prevented from entering themeasurement flow path 32 through the gap between the first housing part151 and the sensor SA 50.

In this case, unintentional change of the shape of the measurement flowpath 32, which is caused by a solidified portion of the molten resinwhich has entered the measurement flow path 32 through the gap betweenthe first housing part 151 and the sensor SA 50, is unlikely to occur.In addition, contact or adhesion of the solidified portion with or tothe flow rate sensor 22 as a foreign matter, which is caused by peelingoff of the solidified portion from the first housing part 151 and thesensor SA 50 in the measurement flow path 32, is also unlikely to occur.Therefore, deterioration in detection accuracy of the flow rate sensor22 due to the molten resin which has entered the measurement flow path32 from the SA container space 150 can be reduced. Therefore, the airflow rate detection accuracy of the flow rate sensor 22 can beincreased, and as a result, the air flow rate measurement accuracy ofthe air flow meter 20 can be increased.

According to the present embodiment, the housing partition 131 makes aloop around the sensor SA 50. In this configuration, the housingpartition 131 can create a state where the outer surface of the sensorSA 50 and the inner surface of the first housing part 151 are in contactwith each other on an entire outer circumference of the sensor SA 50.Therefore, the housing partition 131 can enhance the sealing property inthe entire boundary between the measurement flow path 32 and the SAcontainer space 150.

According to the present embodiment, the housing partition 131 isarranged at a position on the housing step surface 137 closer to thehousing flow path surface 135 than to the housing container surface 136.In this structure, the measurement flow path 32 and the SA containerspace 150 are partitioned by the housing partition 131 at a position asclose as possible to the measurement flow path 32. Thus, a part of thegap between the first housing part 151 and the sensor SA 50 included inthe measurement flow path 32 can be made as small as possible. Here, inthe measurement flow path 32, the gap between the first housing part 151and the sensor SA 50 is a region in which turbulence of airflow islikely to occur due to inflow of air flowing from the measurement inlet35 toward the measurement outlet 36. Therefore, as the gap between thefirst housing part 151 and the sensor SA 50 is smaller, turbulence isless likely to occur in the air flow in the measurement flow path 32,and the detection accuracy of the flow rate sensor 22 is likely to beimproved. Therefore, since the housing partition 131 is provided at aposition as close as possible to the housing flow path surface 135, thedetection accuracy of the flow rate sensor 22 can be improved.

According to the present embodiment, the container angle θ12 is largerthan the flow path angle θ11. In this configuration, when the sensor SA50 is inserted into the SA container space 150 of the first housing part151, the housing partition 131 is likely to be crushed and deformed soas to be folded or collapsed toward the SA container space 150.Therefore, when the housing partition 131 is deformed and brought intocontact with the outer surface of the sensor SA 50, unintentional entryof the crushed dust of the housing partition 131 into the measurementflow path 32 is difficult to occur. As a result, deterioration indetection accuracy of the flow rate sensor 22 due to contact or adhesionof the crushed dust with or to the flow rate sensor 22 in themeasurement flow path 32 can be reduced.

According to the present embodiment, the housing partition 131 providedon the housing step surface 137 is in contact with the SA step surface147. In this configuration, both the housing step surface 137 and the SAstep surface 147 intersect the height direction Y and face each other.Thus, when the sensor SA 50 is inserted into the first housing part 151,the SA step surface 147 is engaged with the housing partition 131.Therefore, the housing partition 131 can be brought into tight contactwith the SA step surface 147 by simply pushing the sensor SA 50 into thefirst housing part 151 toward the measurement flow path 32. As a result,the measurement flow path 32 and the SA container space 150 can becertainly partitioned by the housing partition 131, and an increase inwork load at the time of assembling the sensor SA 50 to the firsthousing part 151 can be suppressed.

In the present embodiment, the housing step surface 137 of the firsthousing part 151 faces to the housing opening 151 a. In thisconfiguration, the SA step surface 147 of the sensor SA 50 can bepressed against the housing step surface 137 by simply pushing thesensor SA 50 inserted into the SA container space 150 through thehousing opening 151 a toward the measurement flow path 32. Therefore,the housing partition 131 of the SA step surface 147 can be easilybrought into tight contact with the housing step surface 137.

<Description of Configuration Group D>

As shown in FIGS. 22 and 23, the measurement flow path 32 is curved sothat the portion between the measurement inlet 35 and the measurementoutlet 36 bulges toward the flow rate sensor 22. The measurement flowpath 32 has a U shape as a whole. In the measurement flow path 32, themeasurement inlet 35 and the measurement outlet 36 are arranged in thedepth direction Z. In this case, the depth direction Z corresponds to anarrangement direction, and the height direction Y is orthogonal to thedepth direction Z. In the measurement flow path 32, the portion betweenthe measurement inlet 35 and the measurement outlet 36 is curved tobulge in the housing basal end direction along the height direction Y.

The inner surface of the housing 21 includes an outer measurement curvedsurface 401 and an inner measurement curved surface 402. The outermeasurement curved surface 401 and the inner measurement curved surface402 extend along the center line CL4 of the measurement flow path 32.The inner surface of the housing 21 includes the front measurement wallsurface 103 and the back measurement wall surface 104 as describedabove, in addition to the outer measurement curved surface 401 and theinner measurement curved surface 402. The outer measurement curvedsurface 401 and the inner measurement curved surface 402 face each otherin the directions Y and Z orthogonal to the width direction X. The outermeasurement curved surface 401 and the inner measurement curved surface402 face each other across the front measurement wall surface 103 andthe back measurement wall surface 104.

The outer measurement curved surface 401 defines an outer outline of acurved part of the measurement flow path 32. The outer measurementcurved surface 401 is provided circumferentially outward of themeasurement flow path 32 and the flow rate sensor 22. The outermeasurement curved surface 401 connects the measurement inlet 35 and themeasurement outlet 36. The outer measurement curved surface 401 isconcavely curved such that the portion between the measurement inlet 35and the measurement outlet 36 is concaved toward the flow rate sensor 22as a whole. The outer measurement curved surface 401 includes themeasurement ceiling surface 102. The SA insertion hole 107 is providedon the outer measurement curved surface 401.

The inner measurement curved surface 402 defines an inner outline of thecurved part of the measurement flow path 32. The inner measurementcurved surface 402 is provided circumferentially inward of themeasurement flow path 32. The inner measurement curved surface 402connects the measurement inlet 35 and the measurement outlet 36. Theinner measurement curved surface 402 is curved such that the portionbetween the measurement inlet 35 and the measurement outlet 36 bulgestoward the flow rate sensor 22 as a whole. The inner measurement curvedsurface 402 does not have a portion concaved in a direction away fromthe outer measurement curved surface 401. The whole of the innermeasurement curved surface 402 is curved in a convex shape so as tobulge toward the outer measurement curved surface 401. The innermeasurement curved surface 402 includes the measurement floor surface101.

As shown in FIG. 23, the measurement flow path 32 includes a sensor path405, an upstream curved path 406, and a downstream curved path 407. Thesensor path 405 is a portion of the measurement flow path 32 where theflow rate sensor 22 is provided. The sensor path 405 extends straight inthe depth direction Z. The sensor path 405 extends in the main flowdirection parallel to the angle setting surface 27 a of the flange 27.The upstream curved path 406 and the downstream curved path 407 arearranged in the depth direction Z. The sensor path 405 is providedbetween the upstream curved path 406 and the downstream curved path 407.The sensor path 405 connects these curved paths 406 and 407.

A surface of the housing 21 defining the sensor path 405 includes atleast a part of the measurement floor surface 101. In this embodiment, alength of the sensor path 405 in the depth direction Z is defined by themeasurement floor surface 101. Specifically, an upstream end part of themeasurement floor surface 101 is included in an upstream end part of thesensor path 405. A downstream end part of the measurement floor surface101 is included in a downstream end part of the sensor path 405. In thiscase, the length of the sensor path 405 in the depth direction Z is thesame as the length of the measurement floor surface 101. The surface ofthe housing 21 defining the sensor path 405 includes not only the partof the measurement floor surface 101 but also a part of the measurementceiling surface 102, a part of the front measurement wall surface 103,and a part of the back measurement wall surface 104. In the presentembodiment, the measurement floor surface 101 extends straight in thedepth direction Z. Since the measurement floor surface 101 extendsstraight in this way, it can be said that the sensor path 405 extendsstraight.

The upstream curved path 406 extends from the sensor path 405 toward themeasurement inlet 35 in the measurement flow path 32. The upstreamcurved path 406 is provided between the sensor path 405 and themeasurement inlet 35. The upstream curved path 406 is curved in thehousing 21 such that the upstream curved path 406 extends from thesensor path 405 toward the measurement inlet 35. A downstream end partof the upstream curved path 406 faces and is open in the depth directionZ to the sensor path 405. An upstream end part of the upstream curvedpath 406 faces and is open in the height direction Y to the measurementinlet 35. In the upstream curved path 406, the open direction of theupstream end part intersects with the open direction of the downstreamend part, and the intersection angle is 90 degrees, for example. Aninner surface of the upstream curved path 406 includes a part of thefront measurement wall surface 103 and a part of the back measurementwall surface 104.

The downstream curved path 407 extends from the sensor path 405 towardthe measurement outlet 36 in the measurement flow path 32. Thedownstream curved path 407 is provided between the sensor path 405 andthe measurement outlet 36. The downstream curved path 407 is curved inthe housing 21 such that the downstream curved path 407 extends from thesensor path 405 toward the measurement outlet 36. An upstream end partof the downstream curved path 407 faces and is open in the depthdirection Z to the sensor path 405. A downstream end part of thedownstream curved path 407 faces and is open in the height direction Yto the measurement outlet 36. In the downstream curved path 407, similarto the upstream curved path 406, the open direction of the upstream endpart intersects with the open direction of the downstream end part, andthe intersection angle is 90 degrees, for example. An inner surface ofthe downstream curved path 407 includes a part of the front measurementwall surface 103 and a part of the back measurement wall surface 104.

In the measurement flow path 32, the sensor path 405 is included in adetection measurement path 353. The upstream curved path 406 ispositioned to extend in the height direction Y across a boundary betweenan introduction measurement path 352 and the detection measurement path353. In this case, the upstream curved path 406 includes a part of theintroduction measurement path 352 and a part of the detectionmeasurement path 353. The downstream curved path 407 is positioned toextend in the height direction Y across a boundary between the detectionmeasurement path 353 and a discharge measurement path 354. In this case,the downstream curved path 407 includes a part of the detectionmeasurement path 353 and a part of the discharge measurement path 354.

The inner surface of the housing 21 includes an upstream outer curvedsurface 411 and an upstream inner curved surface 415 which are surfacesdefining the upstream curved path 406. The upstream outer curved surface411 defines an outer outline of a curved part of the upstream curvedpath 406. The upstream outer curved surface 411 is providedcircumferentially outward of the upstream curved path 406. The upstreamouter curved surface 411 concavely extends along the center line CL4 ofthe measurement flow path 32. The upstream outer curved surface 411 isarched so as to be continuously curved along the center line CL4. Theupstream outer curved surface 411 connects the upstream end part and thedownstream end part of the upstream curved path 406. The upstream outercurved surface 411 corresponds to an upstream outer arched surface.

The upstream inner curved surface 415 defines an inner outline of thecurved part of the upstream curved path 406. The upstream inner curvedsurface 415 is provided circumferentially inward of the upstream curvedpath 406. The upstream inner curved surface 415 convexly extends alongthe center line CL4 of the measurement flow path 32. The downstreaminner curved surface 425 is arched so as to be continuously curved alongthe center line CL4. The upstream inner curved surface 415 connects theupstream end part and the downstream end part of the upstream curvedpath 406. The upstream inner curved surface 415 corresponds to anupstream inner arched surface. The inner surface of the housing 21includes not only the upstream outer curved surface 411 and the upstreaminner curved surface 415 but also a part of the front measurement wallsurface 103 and a part of the back measurement wall surface 104 whichare surfaces defining the upstream curved path 406.

The inner surface of the housing 21 includes a downstream outer curvedsurface 421 and an downstream inner curved surface 425 which aresurfaces defining the downstream curved path 407. The downstream outercurved surface 421 defines an outer outline of a curved part of thedownstream curved path 407. The downstream outer curved surface 421 isprovided circumferentially outward of the downstream curved path 407.The downstream outer curved surface 421 extends along the center lineCL4 of the measurement flow path 32. The downstream outer curved surface421 is bent at a predetermined angle along the center line CL4. Thebending angle of the downstream outer curved surface 421 is, forexample, 90 degrees.

The downstream outer curved surface 421 includes a downstream outerhorizontal surface 422, a downstream outer vertical surface 423, and adownstream outer internal corner 424. The downstream outer horizontalsurface 422 extends straight downstream from the upstream end part ofthe downstream curved path 407 in the depth direction Z. The downstreamouter vertical surface 423 extends straight upstream from the downstreamend part of the downstream curved path 407 in the height direction Y.The downstream outer horizontal surface 422 and the downstream outervertical surface 423 are connected to each other. The downstream outerhorizontal surface 422 and the downstream outer vertical surface 423join inwardly each other to form the downstream outer internal corner424. The downstream outer internal corner 424 has a shape in which thedownstream outer curved surface 421 is bent at a substantially rightangle.

The downstream inner curved surface 425 defines an inner outline of thecurved part of the downstream curved path 407. The downstream innercurved surface 425 is provided circumferentially inward of thedownstream curved path 407. The downstream inner curved surface 425convexly extends along the center line CL4 of the measurement flow path32. The downstream inner curved surface 425 is arched so as to becontinuously curved along the center line CL4. The downstream innercurved surface 425 connects the upstream end part and the downstream endpart of the downstream curved path 407. The downstream inner curvedsurface 425 corresponds to a downstream inner arched surface. The innersurface of the housing 21 includes not only the downstream outer curvedsurface 421 and the downstream inner curved surface 425 but also a partof the front measurement wall surface 103 and a part of the backmeasurement wall surface 104 which are surfaces defining the downstreamcurved path 407.

In the measurement flow path 32, the outer measurement curved surface401 includes the upstream outer curved surface 411 and the downstreamouter curved surface 421. Each of the upstream outer curved surface 411and the downstream outer curved surface 421 includes a part of themeasurement ceiling surface 102. The inner measurement curved surface402 includes not only the above-described measurement floor surface 101but also the upstream inner curved surface 415 and the downstream innercurved surface 425.

In the measurement flow path 32, a degree of bulge of the downstreaminner curved surface 425 in a direction expanding the measurement flowpath 32 is smaller than a degree of bulge of the upstream inner curvedsurface 415 in the direction expanding the measurement flow path 32.Specifically, a length of the downstream inner curved surface 425 islarger than a length of the upstream inner curved surface 415 in adirection in which the center line CL4 of the measurement flow path 32extends. In this case, a radius of curvature R32 of the downstream innercurved surface 425 is larger than a radius of curvature R31 of theupstream inner curved surface 415. That is, there is a relationship ofR32>R31. In other words, the curve of the downstream inner curvedsurface 425 is gentler than the curve of the upstream inner curvedsurface 415.

In the measurement flow path 32, a degree of recess of the downstreamouter curved surface 421 in the direction expanding the measurement flowpath 32 is larger than a degree of recess of the upstream outer curvedsurface 411 in the direction expanding the measurement flow path 32.Specifically, the downstream outer curved surface 421 is bent at a rightangle while the upstream outer curved surface 411 is arched. In thiscase, in the direction in which the center line CL4 of the measurementflow path 32 extends, a length of the bent portion of the downstreamouter curved surface 421 is quite small and is smaller than a length ofthe upstream outer curved surface 411. If a radius of curvature can becalculated for the bent portion of the downstream outer curved surface421, this radius of curvature is substantially zero and is smaller thanthe radius of curvature R33 of the upstream outer curved surface 411. Inthis case, the curve of the downstream outer curved surface 421 issharper than the curve of the upstream outer curved surface 411.

In the upstream curved path 406, the degree of recess of the upstreamouter curved surface 411 in the direction expanding the measurement flowpath 32 is smaller than the degree of bulge of the upstream inner curvedsurface 415 in the direction expanding the measurement flow path 32.Specifically, the length of the upstream outer curved surface 411 islarger than the length of the upstream inner curved surface 415 in thedirection in which the center line CL4 of the measurement flow path 32extends. In this case, the radius of curvature R33 of the upstream outercurved surface 411 is larger than the radius of curvature R31 of theupstream inner curved surface 415. That is, there is a relationship ofR33>R31.

In the downstream curved path 407, the degree of recess of thedownstream outer curved surface 421 in the direction expanding themeasurement flow path 32 is larger than the degree of bulge of thedownstream inner curved surface 425 in the direction expanding themeasurement flow path 32. Specifically, the length of the downstreamouter curved surface 421 is smaller than the length of the downstreaminner curved surface 425 in the direction in which the center line CL4of the measurement flow path 32 extends.

In the downstream curved path 407, the degree of recess of thedownstream outer curved surface 421 is larger than the degree of bulgeof the downstream inner curved surface 425. Thus, a cross sectional areaof the downstream curved path 407 becomes as large as possible in crosssectional area S4 of the measurement flow path 32. Specifically, in adirection orthogonal to both the center line CL4 of the measurement flowpath 32 and the width direction X, a distance L35 b between thedownstream outer curved surface 421 and the downstream inner curvedsurface 425 is larger than a distance L35 a between the upstream outercurved surface 411 and the upstream inner curved surface 415. That is,there is a relationship of L35 b>L35 a.

The distance L35 b between the downstream outer curved surface 421 andthe downstream inner curved surface 425 is a distance at a portion ofthe downstream curved path 407 in which the downstream outer curvedsurface 421 and the downstream inner curved surface 425 are most distantfrom each other. The portion in which the downstream outer curvedsurface 421 and the downstream inner curved surface 425 are most distantfrom each other is, for example, a portion in which the downstream outerinternal corner 424 of the downstream outer curved surface 421 and acenter part of the downstream inner curved surface 425 face each other.The distance L35 a between the upstream outer curved surface 411 and theupstream inner curved surface 415 is a distance at a portion of theupstream curved path 406 in which the upstream outer curved surface 411and the upstream inner curved surface 415 are most distant from eachother. The portion in which the upstream outer curved surface 411 andthe upstream inner curved surface 415 are most distant from each otheris, for example, a portion in which a center part of the upstream outercurved surface 411 and a center part of the upstream inner curvedsurface 415 face each other.

Regarding the measurement flow path 32, an arrangement line CL31 isdefined as an imaginary straight line that passes through the flow ratesensor 22 and extends in the depth direction Z. The arrangement lineCL31 passes through the center CO1 of the heating resistor 71 of theflow rate sensor 22 and is orthogonal to both the center lines CL1 andCL5 of the heating resistor 71. Regarding the arrangement line CL31, thedepth direction Z corresponds to an arrangement direction in which theupstream curved path 406 and the downstream curved path 407 arearranged. In the sensor path 405, the arrangement line CL31 and thecenter line CL4 of the measurement flow path 32 are parallel to eachother. The arrangement line CL31 extends parallel to the angle settingsurface 27 a of the housing 21.

The arrangement line CL31 passes through the sensor path 405, theupstream curved path 406 and the downstream curved path 407 andintersects with the upstream outer curved surface 411 and the downstreamouter curved surface 421. In the downstream outer curved surface 421,the arrangement line CL31 intersects with the downstream outer verticalsurface 423. The sensor path 405 extends straight along the arrangementline CL31. On the arrangement line CL31, a distance L31 b between theflow rate sensor 22 and the downstream outer curved surface 421 islarger than a distance L31 a between the flow rate sensor 22 and theupstream outer curved surface 411. That is, there is a relationship ofL31 b>L31 a. Thus, the flow rate sensor 22 is provided at a positionrelatively near the upstream outer curved surface 411. The distances L31a, L31 b are from the center line CL5 of the heating resistor 71.

In the sensor SA 50, the sensor support 51 is provided at the positionrelatively near to the upstream outer curved surface 411, so that theflow rate sensor 22 is provided at the position relatively near to theupstream outer curved surface 411. On the arrangement line CL31, adistance L32 b between the sensor support 51 and the downstream outercurved surface 421 is larger than a distance L32 a between the sensorsupport 51 and the upstream outer curved surface 411. That is, there isa relationship of L32 b>L32 a. In the measurement flow path 32, also outof the arrangement line CL31, a distance between the sensor support 51and the downstream outer curved surface 421 is larger in the depthdirection Z than a distance between the sensor support 51 and theupstream outer curved surface 411.

In FIG. 23, the distance L32 a is defined as a distance between theupstream outer curved surface 411 and a portion of the molded upstreamsurface 55 c of the sensor support 51 through which the arrangement lineCL31 passes. Further, the distance L32 b is defined as a distancebetween the downstream outer curved surface 421 and a portion of themolded downstream surface 55 d of the sensor support 51 through whichthe arrangement line CL31 passes.

The sensor path 405 is provided between the upstream outer curvedsurface 411 and the downstream outer curved surface 421 at a positionrelatively near to the upstream outer curved surface 411. In this case,on the arrangement line CL31, a distance L33 b between the sensor path405 and the downstream outer curved surface 421 is larger than adistance L33 a between the sensor path 405 and the upstream outer curvedsurface 411. That is, there is a relationship of L33 b>L33 a.

The flow rate sensor 22 is provided at a position relatively near theupstream curved path 406 in the sensor path 405. In this case, on thearrangement line CL31, a distance L34 b between the flow rate sensor 22and the downstream curved path 407 is larger than a distance L34 abetween the flow rate sensor 22 and the upstream curved path 406. Thatis, there is a relationship of L34 b>L34 a. The sum of the distance L34a and the distance L34 b is the length of the sensor path 405 in thedepth direction Z.

As described above, the housing 21 includes the narrowed portions 111,112 shown in FIGS. 24 and 25. These narrowed portions 111, 112 areprovided on the measurement wall surfaces 103, 104, and form a part ofthe measurement wall surfaces 103, 104. FIGS. 24, 25 show an arrangementcross section CS41. The arrangement cross section CS41 is a crosssection that extends along the arrangement line CL41 and extends in adirection in which the measurement wall surfaces 103, 104 face eachother. Further, the arrangement cross section CS41 is orthogonal to theheight direction Y.

The front measurement wall surface 103 includes a front narrowingsurface 431, a front expanding surface 432, a front narrowing upstreamsurface 433, and a front expanding downstream surface 434. The frontnarrowing surface 431 and the front expanding surface 432 are formed bythe front narrowed portion 111 and are included in an outer surface ofthe front narrowed portion 111. That is, the front narrowed portion 111includes the front narrowing surface 431 and the front expanding surface432. In the front narrowed portion 111, the front narrowing surface 431extends in the depth direction Z from the front peak 111 a toward theupstream curved path 406 while the front expanding surface 432 extendsin the depth direction Z from the front peak 111 a toward the downstreamcurved path 407. The front peak 111 a is a boundary between the frontnarrowing surface 431 and the front expanding surface 432.

The front narrowing surface 431 is inclined with respect to the centerline CL4 of the measurement flow path 32 in the detection measurementpath 353. The front narrowing surface 431 faces toward the upstreamouter curved surface 411. The front narrowing surface 431 graduallyreduces and narrows the measurement flow path 32 in a direction from themeasurement inlet 35 toward the flow rate sensor 22. The cross-sectionalarea S4 of the measurement flow path 32 gradually decreases in adirection from an upstream end part of the front narrowing surface 431toward the front peak 111 a. The front narrowing surface 431 is archedsuch that a portion of the front narrowing surface 431 between theupstream end part and a downstream end part of the front narrowingsurface 431 bulges toward the center line CL4 of the measurement flowpath 32.

The front expanding surface 432 is inclined with respect to the centerline CL4 of the measurement flow path 32 in the detection measurementpath 353. The front expanding surface 432 faces toward the downstreamouter curved surface 421. The front expanding surface 432 graduallyexpands the measurement flow path 32 in a direction from the flow ratesensor 22 toward the measurement outlet 36. The cross-sectional area S4of the measurement flow path 32 gradually increases in a direction fromthe front peak 111 a toward a downstream end part of the front expandingsurface 432. The front expanding surface 432 is arched such that aportion of the front expanding surface 432 between an upstream end partand the downstream end part of the front expanding surface 432 bulgestoward the center line CL4 of the measurement flow path 32.

The front narrowing upstream surface 433 extends straight from theupstream end part of the front narrowing surface 431 toward themeasurement inlet 35 parallel to the arrangement line CL31. The frontnarrowing upstream surface 433 is provided between the upstream outercurved surface 411 and the front narrowing surface 431 in the upstreamcurved path 406. The front narrowing upstream surface 433 connects theupstream outer curved surface 411 and the front narrowing surface 431.The front expanding downstream surface 434 extends straight from thedownstream end part of the front expanding surface 432 toward themeasurement outlet 36 parallel to the arrangement line CL31. The frontexpanding downstream surface 434 is provided between the downstreamouter curved surface 421 and the front expanding surface 432 in thedownstream curved path 407. The front expanding downstream surface 434connects the downstream outer curved surface 421 and the front expandingsurface 432. The front narrowing upstream surface 433 and the frontexpanding downstream surface 434 are arranged in the depth direction Zand are coplanar with each other because the positions in the widthdirection X are overlapped.

The back measurement wall surface 104 includes a back narrowing surface441, a back expanding surface 442, a back narrowing upstream surface443, and a back expanding downstream surface 444. The back narrowingsurface 441 and the back expanding surface 442 are formed by the backnarrowed portion 112 and are included in an outer surface of the backnarrowed portion 112. That is, the back narrowed portion 112 includesthe back narrowing surface 441 and the back expanding surface 442. Inthe back narrowed portion 112, the back narrowing surface 441 extends inthe depth direction Z from the back peak 112 a toward the upstreamcurved path 406 while the back expanding surface 442 extends in thedepth direction Z from the back peak 112 a toward the downstream curvedpath 407. The back peak 112 a is a boundary between the back narrowingsurface 441 and the back expanding surface 442.

The back narrowing surface 441 is inclined with respect to the centerline CL4 of the measurement flow path 32 in the detection measurementpath 353. The back narrowing surface 441 faces toward the upstream outercurved surface 411. The back narrowing surface 441 gradually reduces andnarrows the measurement flow path 32 in a direction from the measurementinlet 35 toward the flow rate sensor 22. The cross-sectional area S4 ofthe measurement flow path 32 gradually decreases in a direction from anupstream end part of the back narrowing surface 441 toward the back peak112 a. The back narrowing surface 441 is arched such that a portion ofthe back narrowing surface 441 between the upstream end part and adownstream end part of the front narrowing surface 431 bulges toward thecenter line CL4 of the measurement flow path 32.

The back expanding surface 442 is inclined with respect to the centerline CL4 of the measurement flow path 32 in the detection measurementpath 353. The back expanding surface 442 faces toward the downstreamouter curved surface 421. The back expanding surface 442 graduallyexpands the measurement flow path 32 in a direction from the flow ratesensor 22 toward the measurement outlet 36. The cross-sectional area S4of the measurement flow path 32 gradually increases in a direction fromthe back peak 112 a toward a downstream end part of the back expandingsurface 442. The back expanding surface 442 is arched such that aportion of the back expanding surface 442 between an upstream end partand the downstream end part of the back expanding surface 442 bulgestoward the center line CL4 of the measurement flow path 32.

The back narrowing upstream surface 443 extends straight from theupstream end part of the back narrowing surface 441 toward themeasurement inlet 35 parallel to the arrangement line CL31. The backnarrowing upstream surface 443 is provided between the upstream outercurved surface 411 and the back narrowing surface 441 in the upstreamcurved path 406. The back narrowing upstream surface 443 connects theupstream outer curved surface 411 and the back narrowing surface 441.The back expanding downstream surface 444 extends straight from thedownstream end part of the back expanding surface 442 toward themeasurement outlet 36 parallel to the arrangement line CL31. The backexpanding downstream surface 444 is provided between the downstreamouter curved surface 421 and the back expanding surface 442 in thedownstream curved path 407. The back expanding downstream surface 444connects the downstream outer curved surface 421 and the back expandingsurface 442. The back narrowing upstream surface 443 and the backexpanding downstream surface 444 are arranged in the depth direction Zand are coplanar with each other because the positions in the widthdirection X are overlapped.

The narrowed portions 111, 112 correspond to a measurement narrowedportion. The front narrowing surface 431 and the back narrowing surface441 correspond to a measurement narrowing surface. The front expandingsurface 432 and the back expanding surface 442 correspond to ameasurement expanding surface. As described above, the center CO1 of theheating resistor 71, the front peak 111 a, and the back peak 112 a arealigned in the width direction X. The front peak 111 a and the back peak112 a are located on the center line CL5 of the heating resistor 71.

In the depth direction Z in which the arrangement line CL31 extends, alength W31 a of the front narrowed portion 111 and a length W31 b of theback narrowed portion 112 are the same. In the front narrowed portion111, a length W32 a of the front narrowing surface 431 in the depthdirection Z is smaller than a length W33 a of the front expandingsurface 432 in the depth direction Z. In the back narrowed portion 112,a length W32 b of the back narrowing surface 441 in the depth directionZ is smaller than a length W33 b of the back expanding surface 442 inthe depth direction Z. In the narrowed portions 111, 112, the length W32a of the front narrowing surface 431 and the length W32 b of the backnarrowing surface 441 are the same, and the length W33 a of the frontexpanding surface 432 and the length W33 b of the back expanding surface442 are the same.

The front narrowed portion 111 is provided at a position relatively nearthe upstream curved path 406 in the depth direction Z. In this case, onthe arrangement line CL31, a distance W34 a between the front narrowedportion 111 and the upstream outer curved surface 411 is larger than adistance W35 a between the front narrowed portion 111 and the downstreamouter curved surface 421. The back narrowed portion 112 is, similar tothe front narrowed portion 111, provided at a position relatively nearthe upstream curved path 406 in the depth direction Z. In this case, onthe arrangement line CL31, a distance W34 b between the back narrowedportion 112 and the upstream outer curved surface 411 is larger than adistance W35 b between the back narrowed portion 112 and the downstreamouter curved surface 421.

Regarding the positional relationship between the upstream outer curvedsurface 411 and the narrowed portions 111, 112, the distance W34 a andthe distance W34 b are the same. Regarding the positional relationshipbetween the downstream outer curved surface 421 and the narrowedportions 111, 112, the distance W35 a and the distance W35 b are thesame.

In the measurement flow path 32, the measurement width dimension W1 (seeFIG. 15) between the front measurement wall surface 103 and the backmeasurement wall surface 104 varies depending on the position. Thismeasurement width dimension W1 is different in the sensor path 405, theupstream curved path 406, and the downstream curved path 407. Themeasurement width dimension W1 is not uniform in each of the sensor path405, the upstream curved path 406, and the downstream curved path 407.However, a distance D34 between the front narrowing upstream surface 433and the back narrowing upstream surface 443 in the upstream curved path406 is the same as a distance D38 between the front expanding downstreamsurface 434 and the back expanding downstream surface 444 in thedownstream curved path 407.

The sensor support 51 is provided in the upstream curved path 406 at acentral position between the front narrowing upstream surface 433 andthe back narrowing upstream surface 443. Here, a center line CL32 of thesensor SA50 is defined. The center line CL32 is a straight imaginaryline that passes through the center of the sensor support 51 in thewidth direction X on the center line CL5 of the heating resistor 71. Thecenter line CL32 is orthogonal to the center line CL5 and extends in thedepth direction Z. The center line CL32 is parallel to the arrangementline CL31. In this case, in the upstream curved path 406, a distance D31a between the center line CL32 and the front narrowing upstream surface433 is the same as a distance D31 b between the center line CL32 and theback narrowing upstream surface 443.

The sensor support 51 is provided in the downstream curved path 407 at acentral position between the front expanding downstream surface 434 andthe back expanding downstream surface 444. In the downstream curved path407, a distance D35 a between the center line CL32 and the frontexpanding downstream surface 434 is the same as a distance D35 b betweenthe center line CL32 and the back expanding downstream surface 444.Regarding the positional relationship between the front measurement wallsurface 103 and the sensor support 51, the distance D31 a and thedistance D35 a are the same. Regarding the positional relationshipbetween the back measurement wall surface 104 and the sensor support 51,the distance D31 b and the distance D35 b are the same.

Since front narrowing upstream surface 433 and the front expandingdownstream surface 434 are coplanar with each other in the frontmeasurement wall surface 103, a protrusion height of the front narrowedportion 111 in the upstream curved path 406 and a protrusion height ofthe front narrowed portion 111 in the downstream curved path 407 are thesame. Specifically, a protrusion height D32 a of the front peak 111 awith respect to the front narrowing upstream surface 433 and aprotrusion height D36 a of the front peak 111 a with respect to thefront expanding downstream surface 434 are the same.

A protrusion height of the front narrowing surface 431 with respect tothe front narrowing upstream surface 433 gradually increases in adirection from the front narrowing upstream surface 433 toward the frontpeak 111 a. This increase rate gradually decreases in the direction fromthe front narrowing upstream surface 433 toward the front peak 111 a.Hence, the front narrowing surface 431 is an arched surface. Aprotrusion height of the front expanding surface 432 with respect to thefront expanding downstream surface 434 gradually decreases in adirection from the front peak 111 a toward the front expandingdownstream surface 434. This decrease rate gradually increases in thedirection from the front peak 111 a toward the front expandingdownstream surface 434. Hence, the front expanding surface 432 is anarched surface.

As described above, in the front narrowed portion 111, the length W33 aof the front expanding surface 432 is larger than the length W32 a ofthe front narrowing surface 431. In this case, the decrease rate of theprotrusion height of the front expanding surface 432 from the front peak111 a to the front expanding downstream surface 434 is smaller than theincrease rate of the protrusion height of the front narrowing surface431 from the front narrowing upstream surface 433 to the front peak 111a. The front narrowing surface 431 and the front expanding surface 432form a continuous arched surface. A tangent line of the front narrowingsurface 431 at the front peak 111 a and a tangent line of the frontexpanding surface 432 at the front peak 111 a are both parallel to thearrangement line CL31.

Regarding the front narrowed portion 111, a front narrowing ratio isdefined as a ratio between the length W32 a of the front narrowingsurface 431 and the protrusion height D32 a of a narrowing side of thefront peak 111 a. A front expanding ratio is defined as a ratio betweenthe length W33 a of the front expanding surface 432 and the protrusionheight D36 a of an expanding side of the front peak 111 a. For example,the front narrowing ratio is calculated by dividing the protrusionheight D32 a on the narrowing side by the length W32 a, and the frontexpanding ratio is calculated by dividing the protrusion height D36 a onthe expanding side by the length W33 a. In this case, the frontexpanding ratio is smaller than the front narrowing ratio.

Since back narrowing upstream surface 443 and the back expandingdownstream surface 444 are coplanar with each other in the backmeasurement wall surface 104, a protrusion height of the back narrowedportion 112 in the upstream curved path 406 and a protrusion height ofthe back narrowed portion 112 in the downstream curved path 407 are thesame. Specifically, a protrusion height D32 b of the back peak 112 awith respect to the back narrowing upstream surface 443 and a protrusionheight D36 b of the back peak 112 a with respect to the back expandingdownstream surface 444 are the same.

A protrusion height of the back narrowing surface 441 with respect tothe back narrowing upstream surface 443 gradually increases in adirection from the back narrowing upstream surface 443 toward the backpeak 112 a. This increase rate gradually decreases in the direction fromthe back narrowing upstream surface 443 toward the back peak 112 a.Hence, the back narrowing surface 441 is an arched surface. A protrusionheight of the back expanding surface 442 with respect to the backexpanding downstream surface 444 gradually decreases in a direction fromthe back peak 112 a toward the back expanding downstream surface 444.This decrease rate gradually increases in the direction from the backpeak 112 a toward the back expanding downstream surface 444. Hence, theback expanding surface 442 is an arched surface.

As described above, in the back narrowed portion 112, the length W33 bof the back expanding surface 442 is larger than the length W32 b of theback narrowing surface 441. In this case, the decrease rate of theprotrusion height of the back expanding surface 442 from the back peak112 a to the back expanding downstream surface 444 is smaller than theincrease rate of the protrusion height of the back narrowing surface 441from the back narrowing upstream surface 443 to the back peak 112 a. Theback narrowing surface 441 and the back expanding surface 442 form acontinuous arched surface. A tangent line of the back narrowing surface441 at the back peak 112 a and a tangent line of the back expandingsurface 442 at the back peak 112 a are both parallel to the arrangementline CL31.

Regarding the back narrowed portion 112, a back narrowing ratio isdefined as a ratio between the length W32 b of the back narrowingsurface 441 and the protrusion height D32 b of a narrowing side of theback peak 112 a. A back expanding ratio is defined as a ratio betweenthe length W33 b of the back expanding surface 442 and the protrusionheight D36 b of an expanding side of the back peak 112 a. For example,the back narrowing ratio is calculated by dividing the protrusion heightD36 b on the narrowing side by the length W32 b, and the back expandingratio is calculated by dividing the protrusion height D32 b on theexpanding side by the length W33 b. In this case, the back expandingratio is smaller than the back narrowing ratio.

In a relationship between the front narrowed portion 111 and the backnarrowed portion 112, the front narrowing ratio is larger than the frontexpanding ratio, and the back narrowing ratio is larger than the backexpanding ratio. This is because the protrusion heights D32 a, D36 a ofthe front peak 111 a are larger than the protrusion heights D32 b, D36 bof the back peak 112 a.

Rates at which the narrowed portions 111, 112 reduce the measurementflow path 32 are defined as reduction rates. The reduction rates areproportional to the narrowing ratios. Thus, the larger the frontnarrowing ratio of the front narrowed portion 111, the larger a frontreduction rate at which the front narrowed portion 111 reduces themeasurement flow path 32. For example, the front narrowing ratio and thefront reduction rate have the same value. Similarly, the larger the backnarrowing ratio of the back narrowed portion 112, the larger a backreduction rate at which the back narrowed portion 112 reduces themeasurement flow path 32. Therefore, in the present embodiment, sincethe front narrowing ratio is larger than the back narrowing ratio, thefront reduction rate is larger than the back reduction rate. Forexample, the back narrowing ratio and the back reduction rate have thesame value.

The sensor support 51 is disposed at a center position between the frontmeasurement wall surface 103 and the back measurement wall surface 104in the upstream curved path 406 and the downstream curved path 407.However, the sensor support 51 is located relatively near the frontmeasurement wall surface 103 in the sensor path 405. This is because theprotrusion height of the front narrowed portion 111 on the frontmeasurement wall surface 103 is larger than the protrusion height of theback narrowed portion 112 on the back measurement wall surface 104.Specifically, the protrusion heights D32 a, D36 a of the front peak 111a with respect to the front narrowing upstream surface 433 and the frontexpanding downstream surface 434 are larger than the protrusion heightsD32 b, D36 b of the back peak 112 a with respect to the back narrowingupstream surface 443 and the back expanding downstream surface 444. As aresult, a distance D33 a between the center line CL32 of the sensorsupport 51 and the front peak 111 a is smaller than a distance D33 bbetween the center line CL32 and the back peak 112 a.

The housing 21 includes a measurement partition 451. The measurementpartition 451 is provided between the introduction measurement path 352and the discharge measurement path 354 in the depth direction Z. Themeasurement partition 451 partitions the introduction measurement path352 and the discharge measurement path 354. In addition, the measurementpartition 451 is provided between the through flow path 31 or a branchmeasurement path 351 and the detection measurement path 353 in theheight direction Y. The measurement partition 451 partitions the throughflow path 31 or the branch measurement path 351 and the detectionmeasurement path 353. The measurement partition 451 connects the frontmeasurement wall surface 103 and the back measurement wall surface 104in the width direction X. The measurement partition 451 forms the innermeasurement curved surface 402. An outer surface of the measurementpartition 451 includes the measurement floor surface 101, the upstreaminner curved surface 415, and the inner measurement curved surface 402such as the downstream inner curved surface 425.

The narrowed portions 111, 112 extend from the measurement partition 451toward the measurement ceiling surface 102. The narrowed portions 111,112 do not extend out of the measurement partition 451 in the depthdirection Z toward either the upstream outer curved surface 411 or thedownstream outer curved surface 421. In the depth direction Z, a widthof the measurement partition 451 is equal to or larger than the lengthsW31 a, W31 b of the narrowed portions 111, 112. The narrowed portions111, 112 are provided between the upstream curved path 406 and thedownstream curved path 407. In the present embodiment, the upstream endparts of the narrowed portions 111, 112 are provided in the upstreamcurved path 406. The downstream end parts of the narrowed portions 111,112 are provided in the downstream curved path 407. Even in thisconfiguration, the narrowed portions 111, 112 are provided between theupstream curved path 406 and the downstream curved path 407.

As shown in FIGS. 4 to 7, the through inlet 33 is provided on thehousing upstream surface 21 c, and is open toward an upstream side inthe intake passage 12. Therefore, the main flow in the intake passage 12in the main flow direction is likely to enter the through inlet 33. Thethrough outlet 34 is provided on the housing downstream surface 21 d,and is open toward a downstream side in the intake passage 12.Therefore, the air flowing out of the through outlet 34 is likely toflow downstream together with the main flow in the intake passage 12.

The measurement outlet 36 is provided on both the housing front surface21 e and the housing back surface 21 f. The housing front surface 21 eand the housing back surface 21 f extend along the arrangement lineCL31. The measurement outlet 36 is open in a direction orthogonal to thearrangement line CL31. Therefore, the main flow in the intake passage 12in the main flow direction is less likely to enter the measurementoutlet 36. The air flowing out of the measurement outlet 36 is likely toflow downstream together with the main flow in the intake passage 12.When the main flow passes near the measurement outlet 36 in the intakepassage 12, the air immediately before the measurement outlet 36 in themeasurement flow path 32 is pulled by the main flow, and therefore theair is likely to flow out of the measurement outlet 36. As a result, theair in the measurement flow path 32 easily flows out of the measurementoutlet 36. The width direction X corresponds to the direction orthogonalto the arrangement line CL31.

Next, a flow mode of air flowing through the measurement flow path 32will be described.

As shown in FIG. 23, the air flowing from the through flow path 31 intothe measurement flow path 32 through the measurement inlet 35 includesan outer curving flow AF31 along the outer measurement curved surface401 and an inner curving flow AF32 along the inner measurement curvedsurface 402. As described above, in the measurement flow path 32, theouter measurement curved surface 401 is concavely curved as a whole.Thus, the outer curving flow AF31 is likely to be along the outermeasurement curved surface 401. The inner measurement curved surface 402is convexly curved as a whole. Thus, the inner curving flow AF32 islikely to be along the inner measurement curved surface 402. Further,the outer measurement curved surface 401 and the inner measurementcurved surface 402 are curved in a direction orthogonal to the widthdirection X. The narrowed portions 111, 112 narrow the measurement flowpath 32 in the width direction X. Therefore, in the measurement flowpath 32, airflow turbulence that causes mixing of the outer curving flowAF31 and the inner curving flow AF32 is less likely to occur.

The outer curving flow AF31 that has reached the upstream curved path406 in the measurement flow path 32 changes its flow direction byflowing along the upstream outer curved surface 411. Since the upstreamouter curved surface 411 is curved more gently than the downstream outercurved surface 421, the curve of the upstream outer curved surface 411is sufficiently mild. Hence, turbulence flow such as swirling flow isless likely to occur in the outer curving flow AF31.

As shown in FIG. 25, an airflow through the measurement flow path 32includes a front offset flow AF33 between the sensor support 51 and thefront narrowing surface 431, and a back offset flow AF34 between thesensor support 51 and the back narrowing surface 441. Air of the curvingflows AF31, AF32 that has flowed along the front measurement wallsurface 103 and reached the narrowed portions 111, 112 is likely to beincluded in the front offset flow AF33. Air of the curving flows AF31,AF32 that has flowed along the back measurement wall surface 104 andreached the narrowed portions 111, 112 is likely to be included in theback offset flow AF34.

With respect to the front side of the sensor support 51, a degree ofairflow narrowing by the front narrowing surface 431 gradually increasesin a direction toward the front peak 111 a, and accordingly, an effectof regulating the front offset flow AF33 gradually increases in thedirection toward the front peak 111 a. Moreover, since the protrusionheights D32 a, D36 a of the front peak 111 a are larger than theprotrusion heights D32 b, D36 b of the back peak 112 a, the flowregulating effect of the front narrowing surface 431 is sufficientlyenhanced. As a result, the front offset flow AF33 which has beensufficiently regulated by the front narrowing surface 431 and the sensorsupport 51 reaches the flow rate sensor 22. Therefore, a flow ratedetection accuracy of the flow rate sensor 22 is likely to be high.

The front offset flow AF33 is gradually accelerated toward the frontpeak 111 a. Then, the front offset flow AF33 is jet out of between thefront peak 111 a and the sensor support 51 as a jet flow toward thedownstream curved path 407. This is because an area between the frontnarrowed portion 111 and the sensor support 51 is expanded by the frontexpanding surface 432. If the area between the front expanding surface432 and the sensor support 51 is sharply expanded, there is a concernthat a turbulence such as a vortex is likely to occur due to separationof the front offset flow AF33 from the front expanding surface 432.However, since the length W33 a of the front expanding surface 432 islarger than the length W32 a of the front narrowing surface 431, thearea between the front expanding surface 432 and the sensor support 51is gently expanded. Therefore, separation of the front offset flow AF33from the front expanding surface 432 is unlikely to occur, and aturbulence such as vortex flow is less likely to occur downstream of thefront peak 111 a.

With respect to the back side of the sensor support 51, a degree ofairflow narrowing by the back narrowing surface 441 gradually increasesin a direction toward the back peak 112 a, and accordingly, an effect ofregulating the back offset flow AF34 gradually increases in thedirection toward the back peak 112 a. In this case, the back offset flowAF34 which has been sufficiently regulated by the back narrowing surface441 and the sensor support 51 reaches the back peak 112 a. Therefore, aturbulence is unlikely to occur in the back offset flow AF34 even afterpassing through the back peak 112 a.

The back offset flow AF34 is gradually accelerated toward the back peak112 a. Then, the back offset flow AF34 is jet out of between the backpeak 112 a and the sensor support 51 as a jet flow toward the downstreamcurved path 407. This is because an area between the back narrowedportion 112 and the sensor support 51 is expanded by the back expandingsurface 442. If the area between the back expanding surface 442 and thesensor support 51 is sharply expanded, there is a concern that aturbulence such as a vortex is likely to occur due to separation of theback offset flow AF34 from the back expanding surface 442. However,since the length W33 b of the back expanding surface 442 is larger thanthe length W32 b of the back narrowing surface 441, the area between theback expanding surface 442 and the sensor support 51 is gently expanded.Therefore, separation of the back offset flow AF34 from the backexpanding surface 442 is unlikely to occur, and a turbulence such asvortex flow is less likely to occur downstream of the back peak 112 a.

The front offset flow AF33 and the back offset flow AF34 are expected tojoin together in the sensor path 405 and the downstream curved path 407after passing by the sensor support 51. For example, if the back offsetflow AF34 has turbulence, turbulence of air flow may be generateddownstream of the sensor support 51, and the front offset flow AF33 isdifficult to pass between the front narrowed portion 111 and the sensorsupport 51. In this case, there is a concern that a flow rate and a flowvelocity of the front offset flow AF33 passing through the flow ratesensor 22 become insufficient, and the flow rate detection accuracy ofthe flow rate sensor 22 may decrease. In contrast, in the presentembodiment, the back offset flow AF34 is regulated by the back narrowedportion 112. Thus, generation of turbulence downstream of the sensorsupport 51 caused by turbulence of the back offset flow AF34 flowingpast the sensor support 51 can be reduced.

When the front offset flow AF33 and the back offset flow AF34 aredischarged from between the sensor support 51 and the narrowed portions111, 112 toward the downstream curved path 407, these offset flows AF33,AF34 proceed as a forward flow toward the downstream outer curvedsurface 421 along the arrangement line CL31. When the offset flows AF33,AF34 hit the downstream outer curved surface 421, the offset flows AF33,AF34 may bounce back from downstream outer curved surface 421 and flowbackward in the measurement flow path 32 in a direction toward the flowrate sensor 22. In particular, when hitting the downstream outervertical surface 423, the offset flows AF33, AF34 are likely to flowbackward to the flow rate sensor 22 along the arrangement line CL31. Ifthe backward flow reaches the flow rate sensor 22 against the forwardflow, the direction of air flow detected by the flow rate sensor 22 maybecome opposite to the original flow, and the detection accuracy of theflow rate sensor 22 may decrease. Further, even if the backward flowdoes not reach the flow rate sensor 22, the backward flow causes theforward flow to become difficult to flow downstream. Therefore, the flowrate detected by the flow rate sensor 22 may become smaller than theactual flow rate, and the detection accuracy of the flow rate sensor 22may decrease.

In contrast, in the present embodiment, the flow rate sensor 22 isprovided at a position nearer to the upstream outer curved surface 411than to the downstream outer curved surface 421. Thus, the flow ratesensor 22 is at a position separated as much as possible from thedownstream outer curved surface 421. According to this configuration,the velocity energy of the offset flows AF33, AF34 is likely to decreasebefore the offset flows AF33, AF34 blown out between the sensor support51 and the narrowed portions 111, 112 reach the downstream outer curvedsurface 421. Hence, even if the offset flows AF33, AF34 bounce back fromthe downstream outer curved surface 421 and become the backward flow,the velocity energy of the backward flow is too low to reach the flowrate sensor 22. Further, the farther the flow rate sensor 22 is from thedownstream outer curved surface 421, the longer the distance for thebackward flow to reach the flow rate sensor 22. Thus, the backward flowcan be suppressed from reaching the flow rate sensor 22.

The imaginary line passing through the flow rate sensor 22 is defined asthe arrangement line CL31. Thus, air of the front offset flow AF33 thathas passed through the flow rate sensor 22 is likely to flow along thearrangement line CL31. Therefore, maximum enlargement in distance L31 bbetween the flow rate sensor 22 and the downstream outer curved surface421 on the arrangement line CL31 can maximizes a distance for the air ofthe front offset flow AF33 passing through the flow rate sensor 22 toreach the downstream outer curved surface 421. The arrangement line CL31passes through the downstream outer vertical surface 423 in the presentembodiment. In this configuration, when the air that has passed throughthe flow rate sensor 22 hits the downstream outer vertical surface 423and bounces back, the air is likely to return to the flow rate sensor 22as it is. In such configuration in which the arrangement line CL31passes through the downstream outer vertical surface 423, the maximumenlargement in distance L31 b between the flow rate sensor 22 and thedownstream outer curved surface 421 on the arrangement line CL31 iseffective for suppressing of the backward flow from reaching the flowrate sensor 22.

According to the present embodiment described thus far, the degree ofrecess of the downstream outer curved surface 421 is larger than thedegree of recess of the upstream outer curved surface 411. In thisconfiguration, the cross-sectional area and volume of the downstreamcurved path 407 can be increased as much as possible by increasing thedegree of recess of the downstream outer curved surface 421. Therefore,the pressure loss in air flow through the downstream curved path 407 canbe decreased. As described above, the decrease of the pressure loss inthe downstream curved path 407 reduces occurrence of a clogged-likestate of air in the downstream curved path 407 after passing through theflow rate sensor 22. Thus, it is unlikely to occur that the air passingthrough the flow rate sensor 22 becomes insufficient in volume andvelocity. Therefore, the flow rate detection accuracy of the flow ratesensor 22 can be increased, and as a result, the flow rate measurementaccuracy of the air flow meter 20 can be increased.

Here, in order to increase the cross-sectional area and volume of thedownstream curved path 407 as much as possible, there may be a method ofexpanding the downstream curved path 407 in the width direction X andthe depth direction Z. However, in this method, there is a concern thatthe housing 21 may become large in the width direction X and the depthdirection Z. In this case, air flow in the intake passage 12 may bedisturbed by the housing 21, and the detection accuracy of the flow ratesensor 22 is likely to decrease. Further, in this case, a necessaryamount of resin material for molding the housing 21 increases, and thusa manufacturing cost of the housing 21 tends to increase.

On the other hand, in the present embodiment, the cross-sectional areaand volume of the downstream curved path 407 are increased as much aspossible by increasing the degree of recess of the downstream outercurved surface 421. Hence, the housing 21 can be prevented from becominglarge. In this case, air flow in the intake passage 12 may not bedisturbed by the housing 21, and the detection accuracy of the flow ratesensor 22 can be enhanced. Further, in this case, a necessary amount ofresin material for molding the housing 21 tends to decrease, and thus amanufacturing cost of the housing 21 can be reduced.

According to the present embodiment, the curved portion of thedownstream outer curved surface 421 is formed by the downstream outerinternal corner 424. According to this configuration, the degree ofrecess of the downstream outer curved surface 421 can be maximizedwithout the downstream outer curved surface 421 providing a detour. Thatis, it is possible to realize a configuration in which the downstreamcurved path 407 has the largest cross-sectional area and volume within arange in which the downstream curved path 407 can be expanded by changein shape of the downstream outer curved surface 421.

According to the present embodiment, the distance L35 b between thedownstream outer curved surface 421 and the downstream inner curvedsurface 425 is larger than the distance L35 a between the upstream outercurved surface 411 and the upstream inner curved surface 415. Accordingto this configuration, it is possible to realize a configuration inwhich the downstream outer curved surface 421 and the downstream innercurved surface 425 are separated from each other as far as possible in adirection orthogonal to the center line CL4 of the measurement flow path32. Therefore, unless the downstream curved path 407 or the housing 21is expanded in the width direction X, the cross-sectional area andvolume of the downstream curved path 407 can be increased as much aspossible by the positional relationship between the downstream outercurved surface 421 and the downstream inner curved surface 425.

According to the present embodiment, the degree of bulge of thedownstream inner curved surface 425 is larger than the degree of bulgeof the upstream inner curved surface 415. Therefore, unless thedownstream curved path 407 or the housing 21 is expanded in the widthdirection X, the cross-sectional area and volume of the downstreamcurved path 407 can be increased as much as possible by the shape of thedownstream inner curved surface 425.

According to the present embodiment, the radius of curvature R32 of thedownstream inner curved surface 425 is larger than the radius ofcurvature R31 of the upstream inner curved surface 415. Thus, the degreeof bulge of the downstream inner curved surface 425 is smaller than thedegree of bulge of the upstream inner curved surface 415. In thisconfiguration, while the degree of bulge of the downstream inner curvedsurface 425 is made as small as possible, the air reaching thedownstream curved path 407 from the flow rate sensor 22 easily flowstoward the measurement outlet 36 along an arch of the downstream innercurved surface 425. Therefore, increase in pressure loss in thedownstream curved path 407 due to air disruption in the downstreamcurved path 407 can be reduced by the shape of the downstream innercurved surface 425.

According to the present embodiment, on the arrangement line CL31, thedistance L31 b between the flow rate sensor 22 and the downstream outercurved surface 421 is larger than the distance L31 a between the flowrate sensor 22 and the upstream outer curved surface 411. In thisconfiguration, the flow rate sensor 22 can be placed at a position asfar as possible from the downstream outer curved surface 421 between theupstream outer curved surface 411 and the downstream outer curvedsurface 421. Therefore, even if the air that has passed through the flowrate sensor 22 in the measurement flow path 32 hits the downstream outercurved surface 421 and flows backward in the direction toward the flowrate sensor 22, the backward flow is difficult to reach the flow ratesensor 22. Further, even if a turbulence of air flow due to the backwardflow occurs in the downstream curved path 407, this turbulence hardlyreach the flow rate sensor 22. Therefore, decrease in detection accuracyof the flow rate sensor 22 can be reduced. As a result, an accuracy inmeasurement of the flow rate by the air flow meter 20 can be enhanced.

In order to maximize the distance L31 b between the flow rate sensor 22and the downstream outer curved surface 421, the downstream outer curvedsurface 421 may be separated from the flow rate sensor 22 by extendingthe detection measurement path 353 in the depth direction Z, forexample. However, in this method, there is a concern that the housing 21may become large in the depth direction Z. In contrast, in the presentembodiment, the distance L31 b between the flow rate sensor 22 and thedownstream outer curved surface 421 is maximized by setting the flowrate sensor 22 at a position near the upstream outer curved surface 411in the detection measurement path 353. Accordingly, the housing 21 canbe prevented from becoming large.

According to the present embodiment, the sensor path 405 in which theflow rate sensor 22 is disposed extends along the arrangement line CL31.In this configuration, air flowing along the flow rate sensor 22 islikely to travel straight along the arrangement line CL31. Thus,turbulence of air flow is less likely to occur around the flow ratesensor 22. In this case, a flow velocity of the air around the flow ratesensor 22 is likely to be stabilized. Thus, the detection accuracy ofthe flow rate sensor 22 can be improved. Moreover, the flow rate sensor22 is arranged at a position as far as possible from the downstreamouter curved surface 421. Hence, the turbulence of air flow in thedownstream curved path 407 is less likely to affect the flow rate sensor22. As a result, turbulence of air flow around the flow rate sensor 22can be suppressed. In this case, a flow velocity of the air around theflow rate sensor 22 can be further stabilized. Thus, the detectionaccuracy of the flow rate sensor 22 can be more improved.

According to the present embodiment, in the sensor path 405 extendingalong the arrangement line CL31, the flow rate sensor 22 is provided ata position closer to the upstream curved path 406 than to the downstreamcurved path 407. In this configuration, in the sensor path 405,turbulence of air around the flow rate sensor 22 can be suppressed andthe flow velocity of the air can be stabilized. And further, the flowrate sensor 22 can be arranged at a position as far as possible from thedownstream outer curved surface 421.

According to the present embodiment, on the arrangement line CL31, thesensor support 51 is provided at a position closer to the upstream outercurved surface 411 than to the downstream curved path 407. In thisconfiguration, the sensor support 51 can be arranged at a position asfar as possible from the downstream curved path 407. Hence, turbulenceof air flowing into the downstream curved path 407 due to the presenceof the sensor support 51 can be reduced.

According to the present embodiment, the arrangement line CL31 passesthrough the downstream outer vertical surface 423 of the downstreamouter curved surface 421. In this configuration, the downstream outervertical surface 423 extends straight to upstream from a downstream endpart of the downstream curved path 407. Hence, the arrangement line CL31passes through a farthest part of the downstream outer curved surface421 from the flow rate sensor 22. In this way, the distance for the airpassing through the flow rate sensor 22 to reach the downstream outercurved surface 421 is enlarged as large as possible. As a result, it canbe reduced that the air passing through the flow rate sensor 22 bouncesat the downstream outer curved surface 421 and flows back to the flowrate sensor 22 as backward flow.

According to the present embodiment, since the downstream inner curvedsurface 425 is arched, the distance L35 b between the downstream outercurved surface 421 and the downstream inner curved surface 425 in thedownstream curved path 407 can be increased as much as possible. In thisconfiguration, the downstream inner curved surface 425 is arched, andthus the cross-sectional area of the downstream curved path 407 isincreased as much as possible. The volume of the downstream curved path407 is maximized. Therefore, even if turbulence of air flow occurs inthe downstream curved path 407 due to air bounce on the downstream outercurved surface 421, the air in the downstream curved path 407 easilyflows toward the measurement outlet 36 together with this turbulence.Therefore, it can be more certainly reduced that the backward flowreaches the flow rate sensor 22 from the downstream curved path 407.

According to the present embodiment, the narrowed portions 111, 112 thatgradually narrow and then gradually expand the measurement flow path 32are provided between the upstream end part of the upstream curved path406 and the downstream end part of the downstream curved path 407. Inthis configuration, the air that has passed through the narrowedportions 111, 112 is blown out as a jet flow toward the downstreamcurved path 407 at high velocity. Thus there is a concern that the airis likely to bounce on the downstream outer curved surface 421.Therefore, such arrangement of the flow rate sensor 22 at a position asfar as possible from the downstream outer curved surface 421 iseffective to prevent the air bounded at the downstream outer curvedsurface 421 from reaching the flow rate sensor 22.

According to the present embodiment, in the narrowed portions 111, 112,the lengths W33 a, W33 b of the expanding surfaces 432, 442 are largerthan the length W32 a, W32 b of the narrowing surfaces 431, 441. In thisconfiguration, a degree of expansion and an expansion rate of theexpanding surfaces 432, 442 in the measurement flow path 32 aremoderated so as to prevent turbulence such as separation of air flowcaused by sharp expansion in the measurement flow path 32. As a result,turbulence of flow in the downstream curved path 407 caused by air whichhas passed through the narrowed portions 111, 112 can be reduced.

According to the present embodiment, the narrowed portions 111, 112 areprovided at a position closer to the upstream outer curved surface 411than to the downstream outer curved surface 421. In this configuration,the narrowed portions 111, 112 can be placed at a position as far aspossible from the downstream outer curved surface 421 between theupstream outer curved surface 411 and the downstream outer curvedsurface 421. Therefore, the velocity energy of the air which has passedthrough the narrowed portions 111, 112 at the time of hitting thedownstream outer curved surface 421 can be reduced without enlarging thehousing 21.

According to the present embodiment, the front measurement wall surface103 and the back measurement wall surface 104 face each other throughthe upstream curved path 406. The measurement wall surfaces 103, 104 areprovided with the narrowed portions 111, 112. In this configuration, adirection in which the air curves in the upstream curved path 406 and adirection in which the air is narrowed by the narrowed portions 111, 112are substantially orthogonal to each other. Therefore, when an airflowsuch as the outer curving flow AF31 along the upstream outer curvedsurface 411 and an airflow such as the inner curving flow AF32 along theupstream inner curved surface 415 pass through the narrowed portions111, 112, turbulence caused by mixing of the airflows can be reduced.Therefore, an effect of regulating airflow by the narrowed portions 111,112 can be enhanced.

According to the present embodiment, the upstream outer curved surface411 is arched. In this configuration, a direction of airflow such as theouter curving flow AF31 along the outer measurement curved surface 401is gradually changed by the upstream outer curved surface 411. Thus,turbulence is less likely to be generated in the airflow along theupstream outer curved surface 411. Therefore, turbulence is less likelyto be generated in air flow that reaches the flow rate sensor 22 such asthe outer curving flow AF31. Turbulence is less likely to be generatedalso in air blown toward the downstream curved path 407.

According to the present embodiment, the inner measurement curvedsurface 402 extending along the measurement flow path 32 is curved so asto bulge toward the flow rate sensor 22 as a whole. In thisconfiguration, a concave portion is not formed on the inner measurementcurved surface 402. Thus, air flow such as the inner curving flow AF32along the inner measurement curved surface 402 is prevented fromentering the concave portion and is less likely to cause turbulence suchas vortex. Therefore, turbulence is less likely to be generated in airflow that reaches the flow rate sensor 22 such as the inner curving flowAF32. Turbulence is less likely to be generated also in air blown towardthe downstream curved path 407.

According to the present embodiment, the measurement outlets 36 areprovided on the housing front surface 21 e and the housing back surface21 f of the outer surface of the housing 21. In this configuration, whenair flows along the measurement outlets 36 of the housing front surface21 e and the housing back surface 21 f in the intake passage 12, thisair pulls out air in the measurement flow path 32 to flow out of themeasurement outlet 36. Therefore, even if turbulence of air flow occursin the downstream curved path 407 due to bounce of air or the like, theair flowing outside the housing 21 in the intake passage 12 is used toaccelerate an air flow together with the turbulence of air flow from thedownstream curved path 407 toward the measurement outlet 36.

<Description of Configuration Group E>

As shown in FIGS. 10, 11, 26, the molded upstream surface 55 c of thesensor SA 50 has a molded upstream inclined surface 471. The moldedupstream inclined surface 471 extends obliquely and straightly from theupstream end part of the molded distal end surface 55 a toward themolded basal end surface 55 b, and corresponds to an upstream inclinedportion inclined with respect to the height direction Y. The moldeddownstream surface 55 d has a molded downstream inclined surface 472.The molded downstream inclined surface 472 extends obliquely from thedownstream end part of the molded distal end surface 55 a toward themolded basal end surface 55 b, and corresponds to a downstream inclinedportion inclined with respect to the height direction Y. The moldedupstream inclined surface 471 and the molded downstream inclined surface472 are both inclined with respect to the arrangement cross sectionCS41, and extend through the arrangement cross section CS41 in theheight direction Y.

As shown in FIGS. 26 and 27, a front upstream end 111 b, which is anupstream end of the front narrowed portion 111, is arranged at aboundary between the front narrowing surface 431 and the front narrowingupstream surface 433. A front downstream end 111 c, which is adownstream end of the front narrowed portion 111, is arranged at aboundary between the front expanding surface 432 and the front expandingdownstream surface 434. A back upstream end 112 b, which is an upstreamend of the back narrowed portion 112, is arranged at a boundary betweenthe back narrowing surface 441 and the back narrowing upstream surface443. A back downstream end 112 c, which is a downstream end of the backnarrowed portion 112, is arranged at a boundary between the backexpanding surface 442 and the back expanding downstream surface 444.

The molded upstream inclined surface 471 of the sensor SA 50 is arrangedat a position so as to extend across both the front upstream end 111 bof the front narrowed portion 111 and the back upstream end 112 b of theback narrowed portion 112 in the depth direction Z. An edge of themolded upstream inclined surface 471 facing in the molding distal enddirection is referred to as a distal end edge 471 a, and an edge of themolded upstream inclined surface 471 facing in molding basal enddirection is referred to as a basal end edge 471 b. In this case, thedistal end edge 471 a is provided downstream of the upstream ends 111 b,112 b of the narrowed portions 111, 112 in the depth direction Z. Thebasal end edge 471 b of the molded upstream inclined surface 471 isprovided upstream of the front narrowed portion 111 and the backnarrowed portion 112 in the depth direction Z. The upstream ends 111 b,112 b of the narrowed portions 111, 112 are provided at positions closerin the depth direction Z to the distal end edge 471 a than to the basalend edge 471 b of the molded upstream inclined surface 471.

The molded downstream inclined surface 472 is arranged at a position soas to extend across both the front downstream end 111 c of the frontnarrowed portion 111 and the back downstream end 112 c of the backnarrowed portion 112 in the depth direction Z. An edge of the moldeddownstream inclined surface 472 facing in the molding distal enddirection is referred to as a distal end edge 472 a, and an edge of themolded downstream inclined surface 472 facing in molding basal enddirection is referred to as a basal end edge 472 b. In this case, thedistal end edge 472 a is provided upstream of the downstream ends 111 c,112 c of the narrowed portions 111, 112 in the depth direction Z. Thebasal end edge 472 b of the molded downstream inclined surface 472 isprovided downstream of the narrowed portions 111, 112 in the depthdirection Z. The downstream ends 111 c, 112 c of the narrowed portions111, 112 are provided at positions closer in the depth direction Z tothe distal end edge 472 a than to the basal end edge 472 b of the moldeddownstream inclined surface 472.

As shown in FIG. 27, in the arrangement cross section CS41 of the airflow meter 20, the molded upstream inclined surface 471 of the moldedupstream surface 55 c is provided upstream of the narrowed portions 111,112. In this case, the molded upstream inclined surface 471 is providedbetween the upstream outer curved surface 411 and the upstream ends 111b, 112 b of the narrowed portions 111, 112. In the arrangement crosssection CS41, a distance W41 a between the molded upstream inclinedsurface 471 and the front narrowed portion 111 in the depth direction Zis the same as a distance W41 b between the molded upstream inclinedsurface 471 and the back narrowed portion 112. Further, the distance W41a is smaller than the length W32 a of the front narrowing surface 431,and the distance W41 b is smaller than the length W32 b of the backnarrowing surface 441.

In the arrangement cross section CS41, the molded downstream inclinedsurface 472 of the molded downstream surface 55 d is provided upstreamof the downstream ends 111 c, 112 c of the narrowed portions 111, 112.In this case, in the depth direction Z, the molded downstream inclinedsurface 472 of the molded downstream surface 55 d is provided betweenthe peaks 111 a, 112 a and the downstream ends 111 c, 112 c of thenarrowed portions 111, 112. In the arrangement cross section CS41, adistance W42 a between the molded downstream inclined surface 472 andthe front downstream end 111 c of the front narrowed portion 111 in thedepth direction Z is the same as a distance W42 b between the moldeddownstream inclined surface 472 and the back downstream end 112 c of theback narrowed portion 112. The distance W42 a is smaller than the lengthW33 a of the front expanding surface 432, and the distance W42 b issmaller than the length W33 b of the back expanding surface 442.

A portion of the molded upstream inclined surface 471 of the sensorsupport 51, which is positioned on the arrangement cross section CS41,is at a position aligned with the introduction measurement path 352 inthe height direction Y. This portion is provided downstream of theupstream inner curved surface 415 in the housing downstream direction inthe upstream curved path 406. In the measurement flow path 32, theintroduction measurement path 352 may be referred to as a first section,the detection measurement path 353 may be referred to as a secondsection, and the discharge measurement path 354 may be referred to as athird section. The discharge measurement path 354 includes a portionthat extends straight in the height direction Y and a portion thatextends from the measurement outlet 36 in a direction tilted from theheight direction Y.

The flow rate sensor 22 is arranged according to a position where theflow velocity of air flowing through the measurement flow path 32 is thelargest. More specifically, the flow rate sensor 22 is provided at theposition where the flow velocity of air is the largest. In the presentembodiment, the position where the flow velocity of air is the largestin the measurement flow path 32 is the position where the front peak 111a is provided. The flow rate sensor 22 is positioned to face the frontpeak 111 a.

According to the present embodiment described above, since the narrowedportions 111 is provided in the measurement flow path 32, the airflowing through the measurement flow path 32 can be regulated. Moreover,in the arrangement cross section CS41, the molded upstream surface 55 cof the sensor support 51 is provided upstream of the narrowed portions111, 112. In this configuration, the air that has flowed past the moldedupstream surface 55 c along the arrangement cross section CS41 isregulated by the entire narrowed portions 111, 112 in the arrangementcross section CS41. In this case, even if turbulence of the air flowoccurs due to the air flowing in the measurement flow path 32 andreaching the sensor support 51, this turbulence of the air flow can bereduced by the entire narrowed portions 111, 112. That is, it isunlikely to occur that the flow regulation effect of the narrowedportions 111, 112 decreases by the presence of the sensor support 51.Therefore, deterioration of the flow rate detection accuracy of the flowrate sensor 22 can be reduced, and as a result, the flow ratemeasurement accuracy of the air flow meter 20 can be increased.

According to this embodiment, the molded upstream inclined surface 471is positioned to extend over the upstream ends 111 b, 112 b of thenarrowed portions 111, 112 in the depth direction Z. According to thisconfiguration, it is not necessary to arrange the entire molded upstreaminclined surface 471 and the entire molded upstream surface 55 cupstream of the narrowed portions 111, 112 in the measurement flow path32. Therefore, the sensor support 51 and the molded portion 55 can beminiaturized. Therefore, turbulence of the air flow in the measurementflow path 32 due to increase in size of the sensor support 51 toupstream can be reduced.

Further, a configuration in which the cross-sectional area S4 of themeasurement flow path 32 decreases in a direction from the measurementinlet 35 toward the flow rate sensor 22 is referred to as aconfiguration narrowing the measurement flow path 32. The configurationnarrowing the measurement flow path 32 includes the sensor support 51together with the narrowing surfaces 431, 441. Hence, since the moldedupstream inclined surface 471 is positioned to extend over the upstreamends 111 b, 112 b of the narrowed portions 111, 112 in the depthdirection Z, the sensor support 51 and the narrowed portions 111, 112are capable of continuously narrowing the measurement flow path 32 in adirection toward the flow rate sensor 22. As a result, increase anddecrease in the cross-sectional area S4 of the measurement flow path 32in the direction from the measurement inlet 35 toward the flow ratesensor 22 can be prevented. Thus, deterioration in regulation effect ofthe sensor support 51 and the narrowed portions 111, 112 can besuppressed.

In contrast, for example, if the sensor support 51 and the narrowedportions 111, 112 are separated from each other in an extendingdirection of the measurement flow path 32, the cross-sectional area S4of the flow rate sensor 22 increases between the sensor support 51 andthe narrowed portions 111, 112. That is, the sensor support 51 and thenarrowed portions 111, 112 cannot continuously narrows the measurementflow path 32 in the direction toward the flow rate sensor 22. In thiscase, the cross-sectional area S4 of the measurement flow path 32 mayincrease and decrease in the direction from the measurement inlet 35toward the flow rate sensor 22. Thus, the regulation effect of thesensor support 51 and the narrowed portions 111, 112 may bedeteriorated.

In the configuration in which the molded upstream inclined surface 471is positioned to extend over the upstream ends 111 b, 112 b of thenarrowed portions 111, 112 in the depth direction Z, a volume of thesensor support 51 in the measurement flow path 32 gradually increases inthe direction from the measurement inlet 35 toward the flow rate sensor22. In this case, the sensor support 51 gradually decreases thecross-sectional area S4 of the measurement flow path 32 in the directionfrom the measurement inlet 35 toward the flow rate sensor 22, andthereby can gradually narrow the measurement flow path 32. Therefore,generation of turbulence of the air flow in the measurement flow path 32due to an excessively high degree of narrowing of the sensor support 51can be reduced.

According to the present embodiment, in the arrangement cross sectionCS41, the molded downstream surface 55 d of the sensor support 51 isprovided upstream of the downstream ends 111 c, 112 c of the narrowedportions 111, 112. In this configuration, turbulence of air which hasflowed past the molded downstream surface 55 d of the sensor support 51can be suppressed by the regulation effect of the narrowed portions 111,112. The regulation effect of the narrowed portions 111, 112 exerts bythe expanding surfaces 432, 442 even downstream of the peaks 111 a, 112a. Moreover, in this configuration, the sensor support 51 can beminiaturized as compared with, for example, a configuration in which themolded downstream surface 55 d is arranged downstream of the narrowedportions 111, 112 in the arrangement cross section CS41. Accordingly, itis unlikely to occur that the flow regulation effect of the narrowedportions 111, 112 decreases due to increase in size of the sensorsupport 51.

According to the present embodiment, the molded downstream inclinedsurface 472 is positioned to extend over the downstream ends 111 c, 112c of the narrowed portions 111, 112 in the depth direction Z. Accordingto this configuration, it is not necessary to arrange the entire moldeddownstream inclined surface 472 and the entire molded downstream surface55 d upstream of the downstream ends 111 c, 112 c of the narrowedportions 111, 112 in the measurement flow path 32. Therefore, the sensorsupport 51 and the molded portion 55 can be miniaturized. Therefore,turbulence of the air flow in the measurement flow path 32 due toincrease in size of the sensor support 51 to downstream can be reduced.

Further, a configuration in which the cross-sectional area S4 of themeasurement flow path 32 increases in a direction from the flow ratesensor 22 toward the measurement outlet 36 is referred to as aconfiguration expanding the measurement flow path 32. The configurationexpanding the measurement flow path 32 includes the sensor support 51together with the expanding surfaces 432, 442. Hence, since the moldeddownstream inclined surface 472 is positioned to extend over thedownstream ends 111 c, 112 c of the narrowed portions 111, 112 in thedepth direction Z, the sensor support 51 and the narrowed portions 111,112 are capable of continuously expanding the measurement flow path 32in a direction toward the measurement outlet 36. As a result, increaseand decrease in the cross-sectional area S4 of the measurement flow path32 in the direction from the flow rate sensor 22 toward the measurementoutlet 36 can be prevented. Thus, deterioration in regulation effect ofthe sensor support 51 and the narrowed portions 111, 112 can besuppressed.

According to the present embodiment, in the narrowed portions 111, 112provided downstream of the molded distal end surface 55 a of the sensorsupport 51 in the arrangement cross section CS41, the lengths W33 a, W33b of the expanding surfaces 432, 442 are larger than the length W32 a,W32 b of the narrowing surfaces 431,441. In this configuration, themeasurement flow path 32 is gently expanded toward the measurementoutlet 36 such that turbulence such as separation caused by the narrowedportions 111, 112 excessively expanding the measurement flow path 32does not occur in an air flow that has flowed past the molded distal endsurface 55 a and reached the narrowed portions 111, 112. Therefore, theturbulence of the airflow that has passed by the sensor support 51 andthe narrowed portions 111 and 112 can be reduced.

According to the present embodiment, the front narrowed portion 111 ispositioned on the front measurement wall surface 103 so as to face theflow rate sensor 22. Thus, an air flow along the flow rate sensor 22 canbe further regulated by the front narrowed portion 111 in theconfiguration in which the regulation effect of the front narrowedportion 111 has been improved by positioning of the molded upstreamsurface 55 c upstream of the front narrowed portion 111 in thearrangement cross section CS41.

According to the present embodiment, the back narrowed portion 112 isprovided on a side of the flow rate sensor 22 opposite the frontnarrowed portion 111. Thus, an air flow between the sensor support 51and the back measurement wall surface 104 can be also regulated by theback narrowed portion 112 in the configuration in which the regulationeffect of the front narrowed portion 111 has been improved bypositioning of the molded upstream surface 55 c upstream of the frontnarrowed portion 111 in the arrangement cross section CS41. Therefore,deterioration in detection accuracy of the flow rate sensor 22 due toturbulence of the air flow along the flow rate sensor 22, which iscaused by turbulence of the air flow between the sensor support 51 andthe back measurement wall surface 104, can be reduced.

According to the present embodiment, the sensor support 51 is providedat a position closer to the front narrowed portion 111 than to the backnarrowed portion 112 in the width direction X. Thus, the regulationeffect of the front narrowed portion 111 with respect to the air flowalong the flow rate sensor 22 can be further enhanced in theconfiguration in which the regulation effect of the front narrowedportion 111 has been improved by positioning of the molded upstreamsurface 55 c upstream of the front narrowed portion 111 in thearrangement cross section CS41.

According to the present embodiment, the reduction rate of themeasurement flow path 32 by the front narrowed portion 111 is largerthan the reduction rate of the measurement flow path 32 by the backnarrowed portion 112. Thus, the regulation effect of the front narrowedportion 111 can be enhanced more than the regulation effect of the backnarrowed portion 112 in the configuration in which the regulation effectof the front narrowed portion 111 has been improved by positioning ofthe molded upstream surface 55 c upstream of the front narrowed portion111 in the arrangement cross section CS41. Moreover, it is possible torealize a configuration in which foreign matter such as dust containedin the air flowing toward the flow rate sensor 22 is more likely toenter between the sensor support 51 and the back narrowed portion 112than between the sensor support 51 and the front narrowed portion 111.

According to the present embodiment, the flow rate sensor 22 is arrangedaccording to a position in the measurement flow path 32 where the flowvelocity is the largest. Thus, decrease in velocity and volume of theair flow along the flow rate sensor 22 can be reduced in theconfiguration in which the regulation effect of the front narrowedportion 111 has been improved by positioning of the molded upstreamsurface 55 c upstream of the front narrowed portion 111 in thearrangement cross section CS41.

According to the present embodiment, a portion of the molded upstreamsurface 55 c of the sensor support 51 that is located on the arrangementcross section CS41 is included in the upstream curved path 406. Thus,even if turbulence of air flow generates in the upstream curved path406, this turbulence can be reduced by the narrowed portions 111, 112 inthe configuration in which the regulation effect of the front narrowedportion 111 has been improved by positioning of the molded upstreamsurface 55 c upstream of the front narrowed portion 111 in thearrangement cross section CS41.

According to the present embodiment, the opening area of the measurementoutlet 36 is smaller than the opening area of the measurement inlet 35.Since the measurement outlet 36 is narrower than the measurement inlet35 in this way, it is possible to realize a configuration in which theentire measurement flow path 32 is narrowed toward the measurementoutlet 36. Thus, the regulation effect can be further enhanced in theentire measurement flow path 32 in the configuration in which theregulation effect of the front narrowed portion 111 has been improved bypositioning of the molded upstream surface 55 c upstream of the frontnarrowed portion 111 in the arrangement cross section CS41.

According to the present embodiment, the opening area of the throughoutlet 34 is smaller than the opening area of the through inlet 33.Since the through outlet 34 is narrower than the through inlet 33 inthis way, it is possible to realize a configuration in which the entirethrough flow path 31 is narrowed toward the measurement inlet 35 or thethrough outlet 34. Thus, the regulation effect can be further enhancedin the entire through flow path 31 in the configuration in which theregulation effect of the front narrowed portion 111 has been improved bypositioning of the molded upstream surface 55 c upstream of the frontnarrowed portion 111 in the arrangement cross section CS41.

<Description of Configuration Group H>

As shown in FIG. 3, the housing 21 includes the flange holes 611, 612.The flange holes 611, 612 are provided in the flange 27 and are throughholes that extend through the flange 27 in the height direction Y. Theflange holes 611, 612 are provided at positions separated from eachother in the width direction X and the depth direction Z. In the widthdirection X, the through flow path 31 is arranged between the flangeholes 611, 612. The flange holes 611, 612 include a first flange hole611 provided between the connector 28 and the through flow path 31 inthe width direction X, and a second flange hole 612 facing the firstflange hole 611 across the through flow path 31 in the width directionX.

A flange hole line CL61 is defined as a linear imaginary line passingthrough a center CO61 of the first flange hole 611 and a center CO62 ofthe second flange hole 612. This flange hole line CL61 overlaps thethrough inlet 33 of the through flow path 31. In other words, thethrough inlet 33 is provided between the first flange hole 611 and thesecond flange hole 612 in a plan view of the air flow meter 20 fromabove in the housing basal end direction. Center lines of the screwsinserted into the flange holes 611, 612 extend in the height direction Yand pass through the centers CO61, CO62 of the flange holes 611, 612.

When the housing 21 is fixed to the pipe bosses 14 d with the screws,the center lines of the screws may deviate from the centers CO61, CO62of the flange holes 611, 612 due to the position shifts of the screwswith respect to the flange holes 611, 612. In this case, the housing 21may be displaced in the width direction X and the depth direction Z fromthe screws as axes. However, a portion of the housing 21 that overlapsthe flange hole line CL61 in plan view is difficult to be displaced inthe width direction X and the depth direction Z as compared with otherportions of the housing 21. As described above, since a part of thethrough inlet 33 overlaps the flange hole line CL61 in the plan view,the through inlet 33 is unlikely to be displaced in the intake passage12. Thus, a production error is unlikely to occur in position of thethrough inlet 33 in the intake passage 12, and it is possible to preventease of air flowing into the through inlet 33 in the intake passage 12from varying from product to product. As a result, an accuracy inmeasurement of the flow rate by the air flow meter 20 can be enhanced.

The through inlet 33 is preferably arranged at or close to the center ofthe intake passage 12 in the directions X, Y orthogonal to the depthdirection Z. This is because the center of the intake passage 12 is theposition where the flow rate and the flow velocity are most likely to belarge and the air flow is most likely to be stable.

The flange holes 611, 612 are not provided with metal bushes. In thisconfiguration, the screws is likely to directly contact portions of theflange 27 defining the flange holes 611, 612. The flange holes 611, 612may be provided with metal bushes. In this configuration, the screws ismore likely to contact the bushes than the portions of the flange 27defining the flange holes 611, 612.

As shown in FIG. 28, the housing 21 includes a connector guide 613. Theconnector guide 613 is provided on an outer surface of the connector 28and extends in an opening direction of the connector 28. The connectorguide 613 guides a position of the plug relative to the connector 28when the plug is attached to the connector 28, and guides an insertiondirection of the plug. The connector guide 613 is provided, for example,in a portion of the connector 28 that forms the housing basal endsurface 21 b, and projects most in the housing basal end direction inthe housing 21.

The angle setting surface 27 a of the flange 27 is provided at aposition shifted from the molded portion 55 of the sensor SA 50 in thehousing basal end direction along the height direction Y. According tothis configuration, even if the flange 27 is deformed due to the anglesetting surface 27 a being engaged with the pipe boss 14 d,unintentional change in position of the molded portion 55 due to thedeformation of the flange 27 is unlikely to occur. Therefore,unintentional change of the flow rate sensor 22 in the measurement flowpath 32 can be reduced.

The connector terminal 28 a of the connector 28 is provided at aposition shifted from the molded portion 55 of the sensor SA 50 in thehousing basal end direction along the height direction Y. According tothis configuration, even if the connector terminal 28 a is deformed dueto the plug being connected with the connector terminal 28 a at the timeof attaching the plug to the connector 28, unintentional change inposition of the molded portion 55 due to the deformation of theconnector terminal 28 a is unlikely to occur.

The connector terminal 28 a is provided at a position shifted from theangle setting surface 27 a in the housing basal end direction along theheight direction Y. In this case, a distance H62 between the connectorterminal 28 a and the molded portion 55 in the height direction Y islarger than a distance H61 between the angle setting surface 27 a andthe molded portion 55 in the height direction Y. The connector terminal28 a may not be provided at the position shifted from the angle settingsurface 27 a in the housing basal end direction.

The holding groove 25 a of the seal holder 25 is provided at a positionshifted from the housing partition 131 of the housing 21 in the housingbasal end direction. According to this configuration, even if theholding groove 25 a is deformed due to the seal member 26 contactingboth the inner surface of the holding groove 25 a and the inner surfaceof the pipe flange 14 c, unintentional deformation of the housingpartition 131 due to the deformation of the holding groove 25 a isunlikely to occur. Therefore, unintentional stop of partitioning by thehousing partition 131 between the SA container space 150 and themeasurement flow path 32 can be reduced.

The housing 21 includes an end protection protrusion 615, an upstreamprotection protrusion 616, and a downstream protection protrusion 617.All of these protection protrusions 615 to 617 are protrusions providedon the housing back surface 21 f. The end protection protrusion 615 isprovided at a position shifted from the intake air temperature sensor 23in the housing distal end direction along the height direction Y. Theend protection protrusion 615 does not project more than the intake airtemperature sensor 23 projects in the housing back direction along thewidth direction X. The upstream protection protrusion 616 is provided ata position shifted from the intake air temperature sensor 23 in thehousing upstream direction along the depth direction Z. The downstreamprotection protrusion 617 is provided at a position shifted from theintake air temperature sensor 23 in the housing downstream directionalong the depth direction Z. The upstream protection protrusion 616 andthe downstream protection protrusion 617 project more than the intakeair temperature sensor 23 in the housing back direction along the widthdirection X. The intake air temperature sensor 23 faces the upstreamprotection protrusion 616 and the downstream protection protrusion 617in the housing basal end direction along the height direction Y.

In the height direction Y, a distance H63 between the holding groove 25a and the housing partition 131 is larger than a distance H64 between anend of the end protection protrusion 615 facing in the housing distalend direction and the intake air temperature sensor 23. Further, thedistance H63 is larger than any of the distances H61, H62, and H64.

A connection terminal 620 having the connector terminal 28 a is attachedto the housing 21. As shown in FIGS. 29 and 30, the connection terminal620 includes a lead connection terminal 621, an intake temperatureconnection terminal 622, and an adjustment connection terminal 623 inaddition to the connector terminal 28 a. Multiple lead connectionterminals 621 are provided to the connection terminal 620 and extend inthe height direction Y. The lead connection terminals 621 include aterminal connected to the connector terminal 28 a, a terminal connectedto the intake temperature connection terminal 622, and a terminalconnected to the adjustment connection terminal 623.

The connector terminal 28 a, the intake temperature connection terminal622 and the adjustment connection terminal 623 extend from the leadconnection terminals 621 in the directions X, Z orthogonal to the heightdirection Y. The intake temperature connection terminal 622 is aterminal electrically connected to the lead wire 23 a of the intake airtemperature sensor 23. A free end of the intake temperature connectionterminal 622 is bent and extends in the height direction Y similar tothe lead connection terminals 621. The direction in which the bent endof the intake temperature connection terminal 622 extends is the same asthe direction in which the lead connection terminals 621 extend.Therefore, the intake temperature connection terminal 622 and the leadconnection terminals 621 can be formed by simply bending a base materialof the connection terminal 620 in the same direction. The adjustmentconnection terminal 623 is a terminal for adjusting an output signal orthe like from the connector terminal 28 a, for example, when the airflow meter 20 is manufactured.

The connector terminal 28 a includes a connector base portion 625 and aconnector connection portion 626. The connector base portion 625 is aportion of the connector terminal 28 a extending from the leadconnection terminal 621 and forms a basal end portion of the connectorterminal 28 a. The connector connection portion 626 is a portion of theconnector terminal 28 a extending from the connector base portion 625and forms a distal end portion of the connector terminal 28 a. While theconnector base portion 625 and the connector connection portion 626 havethe same thickness in the height direction Y, the connector base portion625 is larger in width in the depth direction Z than the connectorconnection portion 626. That is, the connector base portion 625 isthicker than the connector connection portion 626.

In this embodiment, three connector terminals 28 a are provided, andthese connector terminals 28 a are parallel to each other and arrangedin the depth direction Z. In one of the three connector terminals 28 awhich is arranged in the middle of them, the connector connectionportion 626 extends from a central position of the connector baseportion 625 in the depth direction Z. In another of the three connectorterminals 28 a which is arranged in one end of them, the connectorconnection portion 626 extends from an edge portion of the connectorbase portion 625 that faces in a direction away from the adjacentconnector terminal 28 a. In this connector terminal 28 a, the connectorbase portion 625 protrudes from the connector connection portion 626toward the adjacent connector terminal 28 a. In another of the threeconnector terminals 28 a which is arranged in another end of them, theconnector connection portion 626 extends from an edge portion of theconnector base portion 625 that faces in a direction away from theadjacent connector terminal 28 a.

A width of the connection terminal 620 in the depth direction Z isdefined by the intake temperature connection terminal 622. Theconnection terminal 620 has two intake temperature connection terminals622, and these connection terminals 620 are arranged in the depthdirection Z. The connection terminal 620 has six lead connectionterminals 621, and these lead connection terminals 621 are arranged inthe depth direction Z. The intake temperature connection terminal 622and the lead connection terminal 621 are arranged in the width directionX. A width of an area where the two intake temperature connectionterminals 622 arranged is larger in the depth direction Z than a widthof an area where the six lead connection terminals 621 are arranged. Inthis case, the area where the six lead connection terminals 621 arearranged is smaller than and does not depart from, in the depthdirection Z, the area where the two intake temperature connectionterminals 622 are arranged.

As shown in FIG. 32, the inner surface of the housing 21 includes afront through wall surface 631 and a back through wall surface 632 inaddition to a through ceiling surface 341 and the through floor surface345 as formation surfaces that form the through flow path 31. The frontthrough wall surface 631 and the back through wall surface 632 are apair of wall surfaces that face each other across the through ceilingsurface 341 and the through floor surface 345, and connect the throughceiling surface 341 and the through floor surface 345. The front throughwall surface 631 extends from the front measurement wall surface 103 inthe housing distal end direction, and the back through wall surface 632extends from the back measurement wall surface 104 in the housing distalend direction.

The inner surface of the housing 21 includes a front through narrowingsurface 635 and a back through narrowing surface 636. The front throughnarrowing surface 635 is included in the front through wall surface 631,and the back through narrowing surface 636 is included in the backthrough wall surface 632. These through narrowing surfaces 635, 636gradually narrow the through flow path 31 so that the cross-sectionalarea of the through flow path 31 gradually decreases in a direction fromthe through inlet 33 toward the through outlet 34. The through narrowingsurfaces 635, 636 are provided between the measurement inlet 35 and thethrough outlet 34 in the through flow path 31. The through narrowingsurfaces 635, 636 connect an outlet ceiling surface 343 and the throughfloor surface 345, and gradually reduce a distance in the widthdirection X between the front through wall surface 631 and the backthrough wall surface 632 in a direction from the measurement inlet 35toward the through outlet 34. The through narrowing surfaces 635, 636are inclined with respect to the depth direction Z in which the centerline of the through flow path 31 extends, and both the through narrowingsurfaces 635, 636 face toward the through inlet 33.

The inner surface of the housing 21 includes a front narrowing peak 637and a back narrowing peak 638. The front narrowing peak 637 is includedin the front through wall surface 631 and is a surface connecting thefront through narrowing surface 635 and the through outlet 34. The backnarrowing peak 638 is included in the back through wall surface 632 andis a surface connecting the back through narrowing surface 636 and thethrough outlet 34. These narrowing peaks 637, 638 extend in the depthdirection Z parallel with the center line of the through flow path 31and face each other.

As shown in FIG. 32, the housing 21 includes a housing outer wall 651.The housing outer wall 651 forms the outer surface of the housing 21 andis a tubular portion extending in the height direction Y. The outersurface of the housing outer wall 651 forms a housing upstream surface21 c, a housing downstream surface 21 d, a housing front surface 21 e,and a housing back surface 21 f. The housing front surface 21 e and thehousing back surface 21 f include a flat surface extending straight inthe depth direction Z and an inclined surface that is inclined withrespect to the flat surface so as to face in the housing upstreamdirection. The measurement outlet 36 is provided on each of the housingfront surface 21 e and the housing back surface 21 f and at a positionextending in the depth direction Z across a boundary between the flatsurface and the inclined surface.

The housing outer wall 651 is provided with a measurement hole 652. Themeasurement hole 652 is provided on each of the housing front surface 21e and the housing back surface 21 f, and the outer ends of thesemeasurement holes 652 define the measurement outlets 36, respectively.The measurement hole 652 extends in the width direction X from themeasurement outlet 36. The measurement hole 652 facing in the housingfront direction is between and connects the measurement outlet 36provided on the housing front surface 21 e and the front measurementwall surface 103. The measurement hole 652 facing in the housing backdirection is between and connects the measurement outlet 36 provided onthe housing back surface 21 f and the back measurement wall surface 104.

An inner surface of the measurement hole 652 includes an upstreamforming surface 661 and a downstream forming surface 662. The upstreamforming surface 661 faces in the housing downstream direction and formsan upstream edge of the measurement hole 652 in the housing upstreamdirection. The downstream forming surface 662 faces in the housingupstream direction and forms a downstream edge of the measurement hole652 in the housing downstream direction. The upstream forming surface661 and the downstream forming surface 662 are between and connect themeasurement outlet 36 and the measurement wall surfaces 103, 104 in thewidth direction X.

The downstream forming surface 662 has a downstream inclined surface 662a and a downstream facing surface 662 b. The downstream inclined surface662 a extends in a direction inclined with respect to the widthdirection X, and extends in the height direction Y while facingobliquely outward. The downstream facing surface 662 b extends in thewidth direction X, and is parallel to and faces the upstream formingsurface 661. A width of the downstream inclined surface 662 a in thewidth direction X is smaller than a width of the upstream formingsurface 661 in the width direction X. On the other hand, the width ofthe downstream inclined surface 662 a in the width direction X is largerthan a width of the downstream facing surface 662 b in the widthdirection X.

In the measurement hole 652, since the downstream inclined surface 662 aof the downstream forming surface 662 faces obliquely outward, the airflowing out of the measurement outlet 36 flows obliquely along thedownstream inclined surface 662 a in the housing downstream direction inthe measurement flow path 32. In this case, the air flowing out from themeasurement outlet 36 flows obliquely with respect to the widthdirection X in the in the housing downstream direction. Therefore, theair easily joins with air flowing in the intake passage 12 in the mainflow direction. Therefore, for example, the turbulence of the airflow isless likely to occur around the measurement outlet 36 as compared with acase where the air flows out from the measurement outlet 36 in the widthdirection X.

Second Embodiment

In the first embodiment, the housing opening 151 a communicating withthe SA container space 150 is provided to the first housing part 151 andfaces in the housing basal end direction. On the other hand, in thesecond embodiment, a base opening 291 a communicating with an SAcontainer space 290 is provided on a base member 291 so as to face inthe housing front direction. In the present embodiment, an air flowmeter 200 is included in the combustion system 10 instead of the airflow meter 20 as a physical quantity measurement device. In the presentembodiment, components denoted by the same reference numerals as thosein the drawings according to the first embodiment and the configurationsnot described are the same as those in the first embodiment, and havethe same operation and effects. In the present embodiment, differencesfrom the first embodiment will be mainly described.

As shown in FIGS. 33 and 34, the air flow meter 200 is provided in theintake passage 12. The air flow meter 200 is a physical quantitymeasurement device that measures a physical quantity, similar to the airflow meter 20 of the first embodiment, and is attached to the pipingunit 14 (refer to FIGS. 2 and 8).

The air flow meter 200 includes an inward portion 200 a positioned inthe intake passage 12 and an outward portion 200 b located outward ofthe pipe flange 14 c without being in the intake passage 12. The inwardportion 200 a and the outward portion 200 b are arranged in the heightdirection Y.

The air flow meter 200 includes a housing 201, and a flow rate sensor202 for detecting a flow rate of an intake air. The housing 201 is madeof, for example, a resin material. The flow rate sensor 202 isaccommodated in the housing 201. The housing 201 of the air flow meter200 is attached to the intake pipe 14 a such that the flow rate sensor202 can come in contact with the intake air flowing through the intakepassage 12.

The housing 21 is attached to the piping unit 14 as an attachmentobject. An outer surface of the housing 201 includes a pair of endsurfaces 201 a and 201 b opposite in the height direction Y. One of thepair of end surfaces 201 a and 201 b included in the inward portion 200a is referred to as a housing distal end surface 201 a, and anotherincluded in the outward portion 200 b is referred to as a housing basalend surface 201 b. The housing distal end surface 201 a and the housingbasal end surface 201 b are orthogonal to the height direction Y.

A surface of the outer surface of the housing 201 facing upstream in theintake passage 12 is referred to as a housing upstream surface 201 c,and a surface of the outer surface of the housing 201 opposite thehousing upstream surface 201 c is referred to as a housing downstreamsurface 201 d. In addition, one of a pair of opposite surfaces of thehousing 201 opposite each other along the housing upstream surface 201 cand the housing basal end surface 201 b is referred to as a housingfront surface 201 e, and the other is referred to as a housing backsurface 201 f. The housing front surface 201 e and a surface of a sensorSA 220 on which the flow rate sensor 202 is provided face in the samedirection.

Regarding the housing 201, a direction in which the housing distal endsurface 201 a faces in the height direction Y is referred to as ahousing distal end direction, and a direction in which the housing basalend surface 201 b faces in the height direction Y is referred to as ahousing basal end direction. Further, a direction in which the housingupstream surface 201 c faces in the depth direction Z is referred to asa housing upstream direction, and a direction in which the housingdownstream surface 201 d faces in the depth direction Z is referred toas a housing downstream direction. Further, a direction in which thehousing front surface 201 e faces in the width direction X is referredto as a housing front direction, and a direction in which the housingback surface 201 f faces in the width direction X is referred to as ahousing back direction.

As shown in FIGS. 33, 34 and 35, the housing 201 includes a seal holder205, a flange 207 and a connector 208. The air flow meter 200 includes aseal member 206, and the seal member 206 is attached to the seal holder205.

The seal holder 205 is provided inside the pipe flange 14 c and holdsthe seal member 206 so as not to be displaced in the height direction Y.The seal holder 205 is included in the inward portion 200 a of the airflow meter 200. The seal member 206 is a member such as an O-ring thatis inside the pipe flange 14 c and seals the intake passage 12. The sealmember 206 is in tight contact with both an outer peripheral surface ofthe seal holder 205 and an inner peripheral surface of the pipe flange14 c. The connector 208 is a protection portion for protecting aconnector terminal 208 a electrically connected to the flow rate sensor202. The connector terminal 208 a is electrically connected to the ECU15. More specifically, an electrical wiring extending from the ECU 15 isconnected to the connector 208 via a plug. For example, the connectorterminal 208 a is electrically and mechanically connected to a plugterminal of the plug. The flange 207 and the connector 208 are includedin the outward portion 200 b of the air flow meter 200.

The housing 201 includes a bypass flow path 210. The bypass flow path210 is provided inside the housing 201. The bypass flow path 210includes at least a part of an internal space of the housing 201. Aninner surface of the housing 201 is a forming surface and forms thebypass flow path 210.

The bypass flow path 210 is disposed in the inward portion 200 a of theair flow meter 200. The bypass flow path 210 includes a through flowpath 211 and a measurement flow path 212. The flow rate sensor 202 andits surrounding portions of the sensor SA 220, which will be describedlater, are in the measurement flow path 212. The through flow path 211is formed by the inner surface of the housing 201. The measurement flowpath 212 is formed by the inner surface of the housing 201 and the outersurface of a part of the sensor SA 220. The intake passage 12 may bereferred to as a main passage, and the bypass flow path 210 may bereferred to as a sub-passage.

The through flow path 211 penetrates through the housing 201 in thedepth direction Z. The through flow path 211 includes a through inlet213 that is an upstream end part of the through flow path 211, and athrough outlet 214 that is a downstream end part of the through flowpath 211. The measurement flow path 212 is a branch flow path branchedfrom an intermediate part of the through flow path 211. The flow ratesensor 202 is provided in the measurement flow path 212. The measurementflow path 212 has a measurement inlet 215 which is an upstream end partof the measurement flow path 212, and a measurement outlet 216 which isa downstream end part of the measurement flow path 212. A boundarybetween the through flow path 211 and the measurement flow path 212 is aportion where the measurement flow path 212 branches from the throughflow path 211. The measurement inlet 215 is included in the boundary.The boundary between the through flow path 211 and the measurement flowpath 212 may also be referred to as a flow path boundary.

The measurement flow path 212 extends from the through flow path 211 inthe housing basal end direction. The measurement flow path 212 isprovided between the through flow path 211 and the housing basal endsurface 201 b. The measurement flow path 212 is curved so that a portionbetween the measurement inlet 215 and the measurement outlet 216 bulgesin the housing basal end direction. The measurement flow path 212includes an arched portion that curves continuously, a bent portion thatbends in a stepwise manner, and a portion that extends straight in theheight direction Y or the depth direction Z.

The air flow meter 200 has a sensor sub-assembly including the flow ratesensor 202, and the sensor sub-assembly is referred to as the sensor SA220. The sensor SA 220 is embedded in the housing 201 while a part ofthe sensor SA 220 extending into the measurement flow path 212. In theair flow meter 200, the sensor SA 220 and the bypass flow path 210 arearranged in the height direction Y. More specifically, the sensor SA 220and the through flow path 211 are arranged in the height direction Y.The sensor SA 220 corresponds to a detection unit. The sensor SA 220 mayalso be referred to as a measurement unit or a sensor package.

The housing 201 includes an upstream wall 231, a downstream wall 232, afront wall 233, a back wall 234, and an end wall 235. The upstream wall231 forms the housing upstream surface 201 c, and the downstream wall232 forms the housing downstream surface 201 d. The front wall 233 formsthe housing front surface 201 e, and the back wall 234 forms the housingback surface 201 f. The upstream wall 231 and the downstream wall 232are provided at positions separated from each other in the depthdirection Z. The front wall 233 and the back wall 234 are provided atpositions separated from each other in the width direction X. Themeasurement flow path 212 and the SA container space 290 described laterare provided between the upstream wall 231 and the downstream wall 232and between the front wall 233 and the back wall 234. The end wall 235forms the housing distal end surface 201 a of the housing, and isprovided at a position separated from the seal holder 205 in the heightdirection Y.

The housing 201 includes a first intermediate wall 236 and a secondintermediate wall 237. The intermediate walls 236, 237 have plate shapesextending in the directions X and Z orthogonal to the height directionY, similarly to the end wall 235. The intermediate walls 236, 237 areprovided between the end wall 235 and the seal holder 205 in the heightdirection Y. The first intermediate wall 236 is provided between the endwall 235 and the second intermediate wall 237. The bypass flow path 210is provided between the first intermediate wall 236 and the end wall235. The first intermediate wall 236 is provided between the measurementflow path 212 and the SA container space 290. The first intermediatewall 236 separates the measurement flow path 212 from the SA containerspace 290 in the height direction Y. The second intermediate wall 237 isprovided between the first intermediate wall 236 and the seal holder205. The second intermediate wall 237 partitions the SA container space290 in the height direction Y.

The first intermediate wall 236 is provided with a first intermediatehole 236 a. The first intermediate hole 236 a penetrates through thefirst intermediate wall 236 in the height direction Y. An innerperipheral surface of the first intermediate wall 236 is included in theinner surface of the housing 201 and extends annularly along acircumferential edge of the first intermediate hole 236 a. A portion ofthe sensor SA 220 provided with the flow rate sensor 202 penetratesthrough the first intermediate hole 236 a in the height direction Y. Asa result, in the sensor SA 220, the molded distal end surface 225 a andthe flow rate sensor 202 are disposed in the measurement flow path 212,and the molded basal end surface 225 b is disposed in the SA containerspace 290.

The second intermediate wall 237 is provided with a second intermediatehole 237 a. The second intermediate hole 237 a penetrates through thesecond intermediate wall 237 in the height direction Y. A lead terminal223 a of the sensor SA 220 described later penetrates through the secondintermediate hole 237 a in the height direction Y. As a result, in thesensor SA 220, a molded portion 225 described later is arranged at aposition shifted from the second intermediate wall 237 in the housingdistal end direction, and at least an end of the lead terminal 223 a isarranged at a position shifted from the second intermediate wall 237 inthe housing basal end direction.

In the SA container space 290, a filler portion (not shown) is filled ina gap between the housing 201 and the sensor SA 220. The filler portionis formed of a thermosetting resin such as an epoxy resin, a urethaneresin, or a silicon resin. The SA container space 290 is filled bypotting with molten resin that is the thermosetting resin in a meltedstate, and the molten resin is solidified as the potting resin to formthe filler portion. The filler portion can also be called a pottingportion or a potting resin portion.

<Description of Configuration Group A>

The sensor SA 220 includes a sensor support 221 in addition to the flowrate sensor 202. The sensor support 221 is attached to the housing 201and supports the flow rate sensor 202. The sensor support 221 includesan SA substrate 223 and the molded portion 225. The SA substrate 223 isa substrate on which the flow rate sensor 202 is mounted. The moldedportion 225 covers at least a part of the flow rate sensor 202 and atleast a part of the SA substrate 223. The SA substrate 223 may also becalled a lead frame.

The molded portion 225 is formed in a plate shape as a whole. The moldedportion 225 includes a pair of end surfaces 225 a and 225 b opposite inthe height direction Y. One of the pair of end surfaces 225 a and 225 bfacing in the housing distal end direction is referred to as a moldeddistal end surface 225 a, and the other facing in the housing basal enddirection is referred to as a molded basal end surface 225 b. The moldeddistal end surface 225 a is an end part of the molded portion 225 and anend part of the sensor support 221, and corresponds to a support end.The molded portion 225 corresponds to a protective resin.

The molded portion 225 includes a pair of surfaces 225 c, 225 d facingeach other across the molded distal end surface 225 a and the moldedbasal end surface 225 b. One of the pair of surfaces 225 c, 225 d isreferred to as a molded upstream surface 225 c, and the other isreferred to as a molded downstream surface 225 d. The sensor SA 220 isarranged inside the housing 201. The molded distal end surface 225 afaces in a direction toward a tip end of the air flow meter 200. Themolded upstream surface 225 c is arranged upstream of the moldeddownstream surface 225 d in the measurement flow path 212.

The molded upstream surface 225 c of the sensor SA 220 is arrangedupstream of the molded downstream surface 225 d in the measurement flowpath 212. A flow direction of air in a part of the measurement flow path212 where the flow rate sensor 202 is disposed is opposite to a flowdirection of air in the intake passage 12 (see FIG. 8). Therefore, themolded upstream surface 225 c is arranged downstream of the moldeddownstream surface 225 d in the intake passage 12. The air flowing alongthe flow rate sensor 202 flows in the depth direction Z, and this depthdirection Z may also be referred to as a flow direction.

In the sensor SA 220, the flow rate sensor 202 is exposed on one side ofthe sensor SA 220. The molded portion 225 includes a plate surfacereferred to as a molded front surface 225 e on the same side as the flowrate sensor 202 being exposed, and a plate surface referred to as amolded back surface 225 f opposite the molded front surface 225 e. Oneof the plate surfaces of the sensor SA 220 is formed by the molded frontsurface 225 e. The molded front surface 225 e corresponds to a supportfront surface, and the molded back surface 225 f corresponds to asupport back surface.

The SA substrate 223 is formed of a metal material or the like in aplate shape as a whole, and is a conductive substrate. A plate surfaceof the SA substrate 223 is orthogonal to the width direction X andextends in the height direction Y and the depth direction Z. The flowrate sensor 202 is mounted on the SA substrate 223. The SA substrate 223forms a lead terminal 223 a connected to the connector terminal 208 a.The SA substrate 223 has a part covered by the molded portion 225 and apart not covered by the molded portion 225, and the part not covered isthe lead terminal 223 a. The lead terminal 223 a projects in the heightdirection Y from the molded basal end surface 225 b. In FIGS. 33 and 34,illustration of the lead terminal 223 a is omitted.

The flow rate sensor 202 has a similar configuration to the flow ratesensor 22 of the first embodiment. The flow rate sensor 202 includesportions and members corresponding to, for example, the sensor recessportion 61 of the flow rate sensor 22, the membrane portion 62, thesensor substrate 65, the sensor film 66, the heating resistor 71, thetemperature measuring resistors 72, 73, the indirectly heated resistor74, and the wires 75 to 77.

<Description of Configuration Group B>

As shown in FIGS. 33 and 34, the housing 201 includes an SA containerspace 290. The SA container space 290 is provided at a position shiftedfrom the bypass flow path 210 in the housing basal end direction. The SAcontainer space 290 houses a part of the sensor SA 220. At least themolded basal end surface 225 b of the sensor SA 220 is housed in the SAcontainer space 290. The measurement flow path 212 and the SA containerspace 290 are arranged in the height direction Y. The sensor SA 220 ispositioned to extend in the height direction Y across a boundary betweenthe measurement flow path 212 and the SA container space 290. At leastthe molded distal end surface 225 a and the flow rate sensor 202 of thesensor SA 220 are housed in the measurement flow path 212. The SAcontainer space 290 corresponds to a container space.

As shown in FIGS. 36 and 37, the housing 201 includes a housingpartition 271. The housing partition 271 is a protrusion provided on theinner peripheral surface of the first intermediate wall 236, andprojects from the first intermediate wall 236 toward the sensor SA 220.A tip end of the housing partition 271 is in contact with the outersurface of the sensor SA 220. The housing partition 271 is between theouter surface of the sensor SA 220 and the inner surface of the housing201 and separates the SA container space 290 from the measurement flowpath 212.

The inner surface of the housing 201 includes a housing flow pathsurface 275, a housing container surface 276, and a housing step surface277. The housing flow path surface 275, the housing container surface276, and the housing step surface 277 extend in a direction intersectingthe height direction Y. Each of the surfaces 275, 276, 277 extends tomake a loop around the sensor SA 220. In the sensor SA 220, similar tothe first embodiment, the center line CL1 a of the heating resistorlinearly extends in the height direction Y. The housing flow pathsurface 275, the housing container surface 276, and the housing stepsurface 277 extend in a circumferential direction around the centerline.

The housing step surface 277 is a wall surface of the first intermediatewall 236 facing in housing basal end direction. The housing step surface277 faces in the housing basal end direction along the height directionY. The housing step surface 277 is inclined with respect to the centerline CL1 a. The housing step surface 277 faces inward in a radialdirection, i.e. in a direction toward the center line CL1 a. The housingstep surface 277 intersects the height direction Y and corresponds to ahousing intersecting surface. In the present embodiment, the housingstep surface 277 is orthogonal to the center line CL1 a. On the innersurface of the housing 201, an external corner between the housing flowpath surface 275 and the housing step surface 277 and an internal cornerbetween the housing container surface 276 and the housing step surface277 are chamfered.

The housing flow path surface 275 is an inner peripheral surface of thefirst intermediate wall 236. The housing flow path surface 275 forms themeasurement flow path 212. The housing flow path surface 275 extendsfrom an inner peripheral edge of the housing step surface 277 in thehousing distal end direction. The housing flow path surface 275 extendsfrom the housing step surface 277 in a direction away from the SAcontainer space 290.

On the other hand, the housing container surface 276 is inner surfacesof the upstream wall 231, the downstream wall 232, the front wall 233,and the back wall 234. The housing container surface 276 forms the SAcontainer space 290. The housing container surface 276 extends from anouter peripheral edge of the housing step surface 277 in the housingbasal end direction. The housing container surface 276 extends from thehousing step surface 277 in a direction away from the measurement flowpath 212. The housing step surface 277 is provided between the housingflow path surface 275 and the housing container surface 276, and forms astep on the inner surface of the housing 201. The housing step surface277 connects the housing flow path surface 275 and the housing containersurface 276.

An outer surface of the molded portion 225 forms the outer surface ofthe sensor SA 220. The outer surface of the sensor SA 220 includes an SAflow path surface 285, an SA container surface 286, and an SA stepsurface 287. The SA flow path surface 285, the SA container surface 286,and the SA step surface 287 extend in a direction intersecting theheight direction Y. Each of the surfaces 285, 286, 287 extends to make aloop on the outer surface of the sensor SA 220. The SA flow path surface285, the SA container surface 286, and the SA step surface 287 extend inthe circumferential direction around the center line CL1 a of theheating resistor.

In the sensor SA 220, the SA step surface 287 is provided between themolded distal end surface 225 a and the molded basal end surface 225 b.The SA step surface 287 faces toward the molded distal end surface 225 ain the height direction Y. The SA step surface 287 is inclined withrespect to the center line CL1 a. The SA step surface 287 faces outwardin a radial direction, i.e. in a direction away from the center line CL1a. The SA step surface 287 intersects the height direction Y andcorresponds to a unit intersecting surface. Further, the SA flow pathsurface 285 corresponds to a unit flow path surface, and the SAcontainer surface 286 corresponds to a unit container surface. In thepresent embodiment, the SA step surface 287 is orthogonal to the centerline CL1 a. On the outer surface of the sensor SA 220, an internalcorner between the SA flow path surface 285 and the SA step surface 287and an external corner between the SA container surface 286 and the SAstep surface 287 are chamfered.

The SA flow path surface 285 forms the measurement flow path 212. The SAflow path surface 285 extends from an inner peripheral edge of the SAstep surface 287 in the molding distal end direction along the heightdirection Y. The SA flow path surface 285 extends from the SA stepsurface 287 in a direction away from the SA container space 290. On theother hand, the SA container surface 286 forms the SA container space290. The SA container surface 286 extends from an outer peripheral edgeof the SA step surface 287 in the molding basal end direction. The SAcontainer surface 286 extends from the SA step surface 287 in adirection away from the measurement flow path 212. The SA step surface287 is provided between the SA flow path surface 285 and the SAcontainer surface 286, and forms a step on the outer surface of thesensor SA 220. The SA step surface 287 connects the SA flow path surface285 and the SA container surface 286.

In the sensor SA 220, the molded upstream surface 225 c, the moldeddownstream surface 225 d, the molded front surface 225 e, and the moldedback surface 225 f form the SA flow path surface 285, the SA containersurface 286, and the SA step surface 287.

In the air flow meter 200, the housing step surface 277 facing in thehousing basal end direction and the SA step surface 287 facing in thehousing distal end direction face each other. Further, the housing flowpath surface 275 facing radially inward and the SA flow path surface 285facing radially outward face each other. Similarly, the housingcontainer surface 276 facing radially inward and the SA containersurface 286 facing radially outward face each other.

The housing partition 271 of the present embodiment is not provided onthe housing step surface 277 as in the first embodiment, but is providedon the housing flow path surface 275. In this case, the housingpartition 271 extends toward the first intermediate hole 236 a in thedirections X and Z intersecting the height direction Y. A center lineCL12 of the housing partition 271 extends linearly in a directionintersecting the height direction Y. In the present embodiment, thecenter line CL12 is orthogonal to the height direction Y. The housingpartition 271, together with the housing flow path surface 275, extendsto make a loop around the sensor SA 220. In this case, the tip end ofthe housing partition 271 forms the first intermediate hole 236 a. Thetip end of the housing partition 271 is the inner peripheral surface ofthe first intermediate hole 236 a. The housing partition 271 has aportion extending in the width direction X and a portion extending inthe depth direction Z. The housing partition 271 has a substantiallyrectangular frame shape as a whole.

The tip end of the housing partition 271 is in contact with the SA flowpath surface 285 of the sensor SA 220. The housing partition 271 and theSA flow path surface 285 are in tight contact with each other, andenhance a sealing property of the part that separates the SA containerspace 290 from the measurement flow path 212. The SA flow path surface285 is flat and extends straight in a direction intersecting the heightdirection Y. In the present embodiment, the housing flow path surface275 and the SA flow path surface 285 extend parallel to each other. Inthis case, the sealing property is improved at the part where the outersurface of the sensor SA 220 and the inner surface of the housing 201because the housing partition 271 is in contact with the SA flow pathsurface 285. The housing flow path surface 275 and the SA flow pathsurface 285 may not be parallel to each other and may be inclined fromeach other.

The housing partition 271 is orthogonal to the housing flow path surface275. In this case, the center line CL12 of the housing partition 271 andthe housing flow path surface 275 are orthogonal to each other. Thehousing partition 271 has a tapered shape. In the present embodiment,the height direction Y is a width direction of the housing partition271. A width of the housing partition 271 in the width directiongradually decreases toward the tip end of the housing partition 271.Each of a pair of lateral surfaces of the housing partition 271 extendsstraight from the housing flow path surface 275. In this case, thehousing partition 271 has a tapered cross section.

The housing partition 271 is provided at a center of the housing flowpath surface 275 in the height direction Y. In this case, a distancebetween the housing partition 271 and an edge of the housing flow pathsurface 275 facing in the housing distal end direction is smaller than adistance between the housing partition 271 and an edge of the housingflow path surface 275 facing in the housing basal end direction. Thehousing partition 271 may be shifted in position on the housing flowpath surface 275 in the housing distal end direction, or may be shiftedin position in the housing basal end direction.

A portion of the housing step surface 277, which is between the housingflow path surface 275 and the housing partition 271, and the housingflow path surface 275 form the measurement flow path 212. A portion ofthe housing step surface 277, which is between the housing containersurface 276 and the housing partition 271, and the housing containersurface 276 form the SA container space 290.

A portion of the SA step surface 287, which is between the SA flow pathsurface 285 and the housing partition 271, and the SA flow path surface285 form the measurement flow path 212. A portion of the SA step surface287, which is between the SA container surface 286 and the housingpartition 271, and the SA container surface 286 form the SA containerspace 290.

As shown in FIG. 38, the housing 201 includes a base member 291 and acover member 292. These base member 291 and cover member 292 areassembled and integrated with each other so as to form the housing 201.The base member 291 in the housing 201 forms the upstream wall 231, thedownstream wall 232, the back wall 234, the end wall 235, the sealholder 205, the flange 207, and the connector 208. The base member 291is a box-shaped member that is open in the housing front direction as awhole. In the base member 291, the base opening 291 a is provided at anopen end which is a front end. The base opening 291 a is defined byrespective front ends of the upstream wall 231, the downstream wall 232,the end wall 235, and the seal holder 205 which are facing in thehousing front direction. The bypass flow path 210 and the SA containerspace 290 are open in the housing front direction through the baseopening 291 a.

The cover member 292 forms the front wall 233 in the housing 201, and isa plate-shaped member as a whole. The cover member 292 is attached tothe open end of the base member 291 and closes the base opening 291 a.In the housing 201, the through flow path 211, the measurement flow path212, and the SA container space 290 are provided between the base member291 and the cover member 292.

In the housing 201, the first intermediate wall 236 includes a firstbase protrusion 295 and a first cover protrusion 297. The first baseprotrusion 295 is a protruding portion that protrudes from the back wall234 of the base member 291 toward the cover member 292. The first baseprotrusion 295 includes a first recess 295 a. The first recess 295 a isa recessed portion provided on an end surface of the first baseprotrusion 295 and extends through the first base protrusion 295 in theheight direction Y. The first cover protrusion 297 is a protrudingportion that protrudes from the front wall 233 of the cover member 292toward the base member 291. The first cover protrusion 297 is inside thefirst recess 295 a. In the first intermediate wall 236, the end surfaceof the first cover protrusion 297 and a bottom surface of the firstrecess 295 a are displaced from each other, and this displacementprovides the first intermediate hole 236 a.

In the housing 201, the second intermediate wall 237 includes a secondbase protrusion 296 and a second cover protrusion 298. The second baseprotrusion 296 is a protruding portion that protrudes from the back wall234 of the base member 291 toward the cover member 292. The second baseprotrusion 296 includes a second recess 296 a. The second recess 296 ais a recessed portion provided on an end surface of the second baseprotrusion 296 and extends through the second base protrusion 296 in theheight direction Y. The second cover protrusion 298 is a protrudingportion that protrudes from the front wall 233 of the cover member 292toward the base member 291. The second cover protrusion 298 is insidethe second recess 296 a. In the second intermediate wall 237, the endsurface of the second cover protrusion 298 and a bottom surface of thesecond recess 296 a are displaced from each other, and this displacementprovides the second intermediate hole 237 a.

The first base protrusion 295 and the second base protrusion 296 areincluded in the base member 291. The base protrusions 295, 296 protrudefrom the back wall 234 of the base member 291 toward the cover member292. The recesses 295 a, 296 a are provided on the end surfaces of thebase protrusions 295, 296. The first recess 295 a is provided at anintermediate position on the first base protrusion 295 in the depthdirection Z. The second recess 296 a is provided at an intermediateposition on the second base protrusion 296 in the depth direction Z.

The first cover protrusion 297 and the second cover protrusion 298 areincluded in the cover member 292. These cover protrusions 297, 298protrude from the front wall 233 of the cover member 292 toward the basemember 291.

The housing partition 271 includes a base protrusion 271 a and a coverprotrusion 271 b. The base protrusion 271 a is included in the basemember 291. The base protrusion 271 a is a protrusion provided on aninner peripheral surface of the first recess 295 a in the first baseprotrusion 295. A part of the base protrusion 271 a provided on thebottom surface of the first recess 295 a extends in the width directionX toward the cover member 292. A pair of parts of the base protrusions271 a provided on a pair of wall surfaces of the first recess 295 a faceeach other and extend in the depth direction Z. A distance between thepair of parts of the base protrusions 271 a facing each other andprovided on the pair of wall surfaces is slightly smaller in the depthdirection Z than a width of a part of the sensor SA 220 that is insertedinto the first recess 295 a.

The cover protrusion 271 b is included in the cover member 292. Thecover protrusion 271 b is a protrusion provided on the end surface ofthe first base protrusion 295 and extends in the width direction Xtoward the base member 291.

Next, referring to FIGS. 38 and 39, a manufacturing method of the airflow meter 200 will be described focusing on a procedure of mounting thesensor SA 220 to the housing 201.

A manufacturing process of the air flow meter 200 includes a step ofmanufacturing the sensor SA 220, a step of manufacturing the base member291, and a step of manufacturing the cover member 292. After thesesteps, a step of assembling the sensor SA 220, the base member 291, andthe cover member 292 with each other is performed.

At the step of manufacturing the sensor SA 220, the molded portion 225of the sensor SA 220 is manufactured by resin molding using an injectionmolding machine or an injection molding device provided with a molddevice. At this step, similar to the step of manufacturing the moldedportion 55 of the first embodiment, a molten resin obtained by melting aresin material is injected from an injection molding machine andpress-fitted into the mold device. Further, at this step, an epoxythermosetting resin such as an epoxy resin is used as the resin materialfor forming the molded portion 225.

At the step of manufacturing the base member 291, the base member 291 ismanufactured by resin molding or the like using an injection moldingdevice or the like. At the step of manufacturing the cover member 292,the cover member 292 is manufactured by resin molding or the like usingan injection molding device or the like. At these steps, a thermoplasticresin such as polybutylene terephthalate (PBT) or polyphenylene sulfide(PPS) is used as the resin material forming the base member 291 and thecover member 292. The base member 291 and the cover member 292 formed ofthe thermoplastic resin as described above is softer than the moldedportion 225 formed of the thermosetting resin. In other words, the basemember 291 and the cover member 292 have lower hardness and higherflexibility than the molded portion 225.

At the step of assembling the sensor SA 220, the base member 291, andthe cover member 292, first, in FIG. 38, the sensor SA 220 is firstinserted into the base member 291 through the base opening 291 a. Inthis work, the SA flow path surface 285 of the sensor SA 220 is insertedinto the first recess 295 a, and the lead terminal 223 a is insertedinto the second recess 296 a. Accordingly, the sensor SA 220 is fixedbetween the first base protrusion 295 and the second base protrusion296. After the SA flow path surface 285 of the sensor SA 220 contactsthe base protrusion 271 a of the first base protrusion 295, the sensorSA 220 is further pushed toward the back wall 234 into the base member291. In this case, since the hardness of the base member 291 is lowerthan the hardness of the molded portion 225, the tip end of the baseprotrusion 271 a is deformed so as to be pressed in the housing backdirection and crushed by the SA flow path surface 285.

As described above, the inner peripheral surface of the first recess 295a of the base member 291 has the pair of parts of the base protrusion271 a provided on the pair of wall surfaces facing each other. In thisconfiguration, by simply fitting the sensor SA 220 between the pair ofwall surfaces, the sensor SA 220 scrapes the tip portions of the baseprotrusion 271 a on the wall surfaces at the SA flow path surface 285,and accordingly, the base protrusion 271 a on the wall surfaces isdeformed. As a result, the tip portions of the base protrusion 271 a arescraped and newly form end surfaces which are easily comes into contactwith the SA flow path surface 285 of the sensor SA 220.

When the sensor SA 220 is pushed into the first recess 295 a, the SAflow path surface 285 of the sensor SA 220 pushes the base protrusion271 a toward the back wall 234 and crushes the base protrusion 271 a onthe bottom surface of the inner peripheral surface of the first recess295 a. In this case, the tip portion of the base protrusion 271 a on thebottom surface is deformed via crushing by the SA flow path surface 285,and the tip portion of the base protrusion 271 a is crushed and newlyform the end surfaces which are easily comes into contact with the SAflow path surface 285 of the sensor SA 220.

Further, as described above, the cover protrusion 271 b is provided onthe end surface of the first cover protrusion 297 in the cover member292. In this configuration, when the cover member 292 is assembled tothe base member 291, the cover protrusion 271 b of the cover member 292is pressed against the SA flow path surface 285 of the sensor SA 220.Therefore, the cover member 292 is pressed against the base member 291such that the tip portion of the cover protrusion 271 b of the firstcover protrusion 297 is deformed via crushing by the SA flow pathsurface 285. In this case, the tip portion of the cover protrusion 271 bis crushed and newly forms an end surface which is easily comes intocontact with the SA flow path surface 285 of the sensor SA 220.

Then, a work of attaching the cover member 292 to the base member 291 isperformed such that cover member 292 covers the base opening 291 a andthe sensor SA 220. In this work, the first cover protrusion 297 of thecover member 292 is inserted into the first recess 295 a. The coverprotrusion 271 b on the end surface of the first cover protrusion 297contacts the SA flow path surface 285 of the sensor SA220, and then thecover member 292 is further pressed against the sensor SA 220 toward theinside of the base member 291. In this case, since the hardness of thecover member 292 is lower than the hardness of the molded portion 225,the tip end of the cover protrusion 271 b is deformed so as to bepressed in the housing front direction and crushed by the SA flow pathsurface 285. As a result, the end surface of the cover protrusion 271 bin the crushed state is easily brought into contact with the SA flowpath surface 285, and the sealing property between the cover protrusion271 b and the SA flow path surface 285 is improved.

In the above first embodiment, the crushed portion of the housingpartition 131 is illustrated by the chain double-dashed line in FIG. 17.In contrast, in the present embodiment, the portions of the baseprotrusion 271 a and the cover protrusion 271 b crushed by the sensor SA220 are not shown by chain double-dashed line.

After that, the sensor SA 220 is fixed to the base member 291 and thecover member 292 by joining portions of the sensor SA 220 that are incontact with the base member 291 and the cover member 292 with anadhesive or the like. Accordingly, integration of the base member 291and the cover member 292 provides the housing 201. Further, in thiscase, the base protrusion 271 a and the cover protrusion 271 b form thehousing partition 271.

According to the present embodiment described above, the housingpartition 271 protruding from the inner surface of the housing 201 isbetween the sensor SA 220 and the housing 201 and separates themeasurement flow path 212 from the SA container space 290. In thisconfiguration, since the tip end of the housing partition 271 and thesensor SA 220 easily come into contact with each other, a gap isunlikely to be formed between the inner surface of the housing 201 andthe outer surface of the sensor SA 220. When the molten potting resin isinjected into the SA container space 290 of the housing 201 for formingthe filler portion, the potting resin is prevented from entering themeasurement flow path 212 through the gap between the housing 201 andthe sensor SA 220.

In this case, unintentional change of the shape of the measurement flowpath 212, which is caused by a solidified portion of the molten resinwhich has entered the measurement flow path 212 through the gap betweenthe housing 201 and the sensor SA 220, is unlikely to occur. Inaddition, contact or adhesion of the solidified portion with or to theflow rate sensor 202 as a foreign matter, which is caused by peeling offof the solidified portion from the housing 201 and the sensor SA 220 inthe measurement flow path 212, is also unlikely to occur. Therefore,deterioration in detection accuracy of the flow rate sensor 202 due tothe molten resin which has entered the measurement flow path 212 fromthe SA container space 290 can be reduced. Therefore, the air flow ratedetection accuracy of the flow rate sensor 202 can be increased, and asa result, the air flow rate measurement accuracy of the air flow meter200 can be increased.

According to the present embodiment, the housing partition 271 makes aloop around the sensor SA 220. In this configuration, the housingpartition 271 can create a state where the outer surface of the sensorSA 220 and the inner surface of the housing 201 are in contact with eachother on an entire outer circumference of the sensor SA 220. Therefore,the housing partition 271 can enhance the sealing property in the entireboundary between the measurement flow path 212 and the SA containerspace 290.

In the present embodiment, the housing partition 271 is provided on thehousing flow path surface 275. In this structure, the measurement flowpath 212 and the SA container space 290 are partitioned by the housingpartition 271 at a position as close as possible to the measurement flowpath 212. Thus, a part of the gap between the housing 201 and the sensorSA 220 included in the measurement flow path 212 can be made as small aspossible. Here, in the measurement flow path 212, the gap between thehousing 201 and the sensor SA 220 is a region in which turbulence ofairflow is likely to occur due to inflow of air flowing from themeasurement inlet 215 toward the measurement outlet 216. Therefore, asthe gap between the housing 201 and the sensor SA 220 is smaller,turbulence is less likely to occur in the air flow in the measurementflow path 212, and the detection accuracy of the flow rate sensor 202 islikely to be improved. Therefore, since the housing partition 271 isprovided on the housing flow path surface 275, the detection accuracy ofthe flow rate sensor 202 can be improved.

Third Embodiment

In the above-described first embodiment, the through flow path 31 is notsubstantially narrowed in the height direction Y between the throughinlet 33 and the measurement inlet 35. However, in a third embodiment, athrough flow path 31 is narrowed in the height direction Y between athrough inlet 33 and a measurement inlet 35. In the present embodiment,components denoted by the same reference numerals as those in thedrawings according to the first embodiment and the configurations notdescribed are the same as those in the first embodiment, and have thesame operation and effects. In the present embodiment, differences fromthe first embodiment will be mainly described.

<Description of Configuration Group C>

As shown in FIGS. 40 and 41, the through flow path 31 includes an inletthrough path 331, an outlet through path 332, and a branch through path333. The inlet through path 331 extends from the through inlet 33 towarda through outlet 34 and is between and connects the through inlet 33 andan upstream end of the measurement inlet 35. The outlet through path 332extends from the through outlet 34 toward the through inlet 33 and isbetween and connects the through outlet 34 and a downstream end of themeasurement inlet 35. The branch through path 333 is provided betweenthe inlet through path 331 and the outlet through path 332, and connectsthe inlet through path 331 and the outlet through path 332. The branchthrough path 333 extends in the depth direction Z along the measurementinlet 35 and is a portion of the through flow path 31 from which themeasurement flow path 32 is branched. The branch through path 333extends from the measurement inlet 35 in the housing distal enddirection.

The inner surface of the housing 21 includes a through ceiling surface341 and the through floor surface 345 as formation surfaces that formthe through flow path 31. The through ceiling surface 341 and thethrough floor surface 345 face each other in the height direction Y, andthe through flow path 31 is provided between the through ceiling surface341 and the through floor surface 345. The through ceiling surface 341and the through floor surface 345 are between and connect the throughinlet 33 and the through outlet 34. Both the through ceiling surface 341and the through floor surface 345 intersect the height direction Y andextend in the width direction X and the depth direction Z. A measurementoutlet 36 is provided on the through ceiling surface 341.

The through ceiling surface 341 includes an inlet ceiling surface 342and an outlet ceiling surface 343. The inlet ceiling surface 342 forms aceiling surface of the inlet through path 331, and is between andconnects the through inlet 33 and the upstream end of the measurementinlet 35 in the depth direction Z. In this case, the depth direction Zcorresponds to a direction in which the through inlet 33 and the throughoutlet 34 are arranged. The inlet ceiling surface 342 extends straightfrom the through inlet 33 toward the upstream end of the measurementinlet 35. The outlet ceiling surface 343 forms a ceiling surface of theoutlet through path 332, and is between and connects the through outlet34 and the downstream end of the measurement inlet 35. The outletceiling surface 343 extends straight from the through outlet 34 towardthe downstream end of the measurement inlet 35.

The through floor surface 345 includes an inlet floor surface 346, anoutlet floor surface 347, and a branch floor surface 348. The inletfloor surface 346 forms a floor surface of the inlet through path 331,and extends from the through inlet 33 toward the through outlet 34. Theinlet floor surface 346 and the inlet ceiling surface 342 face eachother through the inlet through path 331 and the through inlet 33. Theoutlet floor surface 347 forms a floor surface of the outlet throughpath 332, and extends from the through outlet 34 toward the throughinlet 33. The outlet floor surface 347 and the outlet ceiling surface343 face each other through the outlet through path 332 and the throughoutlet 34. The branch floor surface 348 forms a floor surface of thebranch through path 333. The branch floor surface 348 is providedbetween the inlet floor surface 346 and the outlet floor surface 347,and connects inlet floor surface 346 and the outlet floor surface 347.The branch floor surface 348 faces the measurement inlet 35 via thebranch through path 333.

The inlet ceiling surface 342 and the outlet ceiling surface 343 bothextend straight in the depth direction Z and are parallel to each other.These ceiling surfaces 342, 343 both extend straight in the widthdirection X and are parallel to each other. The through floor surface345 extends straight in the depth direction Z and is parallel to theceiling surfaces 342, 343. The through floor surface 345 extendsstraight in the width direction X and is parallel to the ceilingsurfaces 342, 343. Accordingly, the ceiling surfaces 342, 343 and thethrough floor surface 345 extend straight in the width direction X, andthrough wall surfaces 631, 632 (see FIG. 31) described later extendstraight in the height direction Y. Due to these facts, the throughinlet 33 and the through outlet 34 have rectangular shapes.

The inlet ceiling surface 342, the outlet ceiling surface 343, and thethrough floor surface 345 may be curved such that a portion between anupstream end and a downstream end in the depth direction Z is concave orconvex. The inlet ceiling surface 342, the outlet ceiling surface 343,and the through floor surface 345 may be curved so that a portionbetween the through wall surfaces 631, 632 in the width direction X isconcave or convex. As described above, the through inlet 33 and thethrough outlet 34 may be curved so that at least one side is concave orconvex. That is, the through inlet 33 and the through outlet 34 may notbe rectangular. For example, sides of the through inlet 33 and sides ofthe through outlet 34 along the width direction X may have a curvedconvex shape. The inlet ceiling surface 342, the outlet ceiling surface343, and the through floor surface 345 may be curved so that a portionbetween the through wall surfaces 631, 632 is convex.

The inlet ceiling surface 342 is inclined with respect to the inletfloor surface 346 such that the inlet ceiling surface 342 faces to thethrough inlet 33. An inclination angle θ21 of the inlet ceiling surface342 with respect to the inlet floor surface 346 is more than or equal to10 degrees. That is, the inclination angle θ21 is a value same as 10degrees or a value larger than 10 degrees. There is a relationship:θ21≥10°. As shown in FIG. 41, a floor parallel line CL21 is defined asan imaginary straight line extending parallel to the inlet floor surface346. The inclination angle θ21 is between the inlet ceiling surface 342facing the through inlet 33 and the floor parallel line CL21. In thethrough ceiling surface 341, the inlet ceiling surface 342 and theoutlet ceiling surface 343 are different in inclination angle withrespect to the floor parallel line CL21. Specifically, the inclinationangle θ21 of the inlet ceiling surface 342 with respect to the floorparallel line CL21 is larger than an inclination angle of the outletceiling surface 343 with respect to the floor parallel line CL21.

The inlet ceiling surface 342 corresponds to a ceiling inclined surface.A configuration of the present embodiment is basically the same as theconfiguration of the first embodiment except for a configuration inwhich the inlet ceiling surface 342 faces the through inlet 33. Thedescriptions of the same configuration of the present embodiment is alsothe descriptions of the above first embodiment.

In the inlet through path 331, a distance H21 between the inlet ceilingsurface 342 and the inlet floor surface 346 in the height direction Ygradually decreases in a direction from the through inlet 33 to thethrough outlet 34. The height direction Y here is a direction orthogonalto the main flow line CL22. The reduction rate of the distance H21 is aconstant value in the inlet through path 331.

The through floor surface 345 extends straight in the depth direction Z.In the through floor surface 345, the inlet floor surface 346, theoutlet floor surface 347, and the branch floor surface 348 are coplanarwith each other. As shown in FIG. 41, the main flow line CL22 is definedas an imaginary straight line extending in the depth direction Z that isthe main flow direction. The through floor surface 345 is inclined withrespect to the main flow line CL22 so as to face the through inlet 33.There is. In this case, each of the inlet floor surface 346, the outletfloor surface 347, and the branch floor surface 348 is inclined withrespect to the main flow line CL22. As described above, the main flowline CL22 extends parallel to the angle setting surface 27 a because theangle setting surface 27 a of the flange 27 extends in the main flowdirection.

Not only the inlet floor surface 346 but also the inlet ceiling surface342 is inclined with respect to the main flow line CL22. An inclinationangle θ22 of the inlet ceiling surface 342 with respect to the main flowline CL22 is more than or equal to 10 degrees, similar to theinclination angle θ21. That is, the inclination angle θ22 is a valuesame as 10 degrees or a value larger than 10 degrees. There is arelationship: θ22≥10°. In the present embodiment, the inclination angleθ22 is set to, for example, 10 degrees. As shown in FIG. 41, theinclination angle θ22 is between the inlet ceiling surface 342 facingthe through inlet 33 and the main flow line CL22. The inclination angleθ22 of the inlet ceiling surface 342 with respect to the main flow lineCL22 is smaller than the inclination angle θ21 of the inlet ceilingsurface 342 with respect to the inlet floor surface 346.

The inlet through path 331 has a shape that is gradually narrowed in adirection from the through inlet 33 toward the through outlet 34 by atleast the inlet ceiling surface 342 and the inlet floor surface 346. Inthis case, as shown in FIG. 42, a cross-sectional area S21 of the inletthrough path 331 in the directions X, Y orthogonal to the main flow lineCL22 gradually decreases in the direction from the through inlet 33toward the through outlet 34. The cross-sectional area S21 has a largestvalue at the through inlet 33 which is an upstream end of the inletthrough path 331, and has a smallest value at a downstream end of theinlet through path 331. A reduction rate of the cross-sectional area S21is a constant value in the inlet through path 331, and a graph showingthe value of the cross-sectional area S21 in the inlet through path 331extends linearly as shown in FIG. 42.

The outlet through path 332 has a shape that is gradually narrowed in adirection from an upstream end of the outlet through path 332 toward thethrough outlet 34. In this case, a cross-sectional area of the outletthrough path 332 in the directions X, Y orthogonal to the main flow lineCL22 gradually decreases in the direction from the upstream end of theoutlet through path 332 toward the through outlet 34. Thecross-sectional area of the inlet through path 331 can also be referredto as a flow path area of the inlet through path 331.

As shown in FIG. 40, the measurement flow path 32 has a folded shapefolded back between the measurement inlet 35 and the measurement outlet36. The measurement flow path 32 includes a branch measurement path 351,an introduction measurement path 352, a detection measurement path 353,and a discharge measurement path 354. In the measurement flow path 32,the branch measurement path 351, the introduction measurement path 352,the detection measurement path 353, and the discharge measurement path354 are arranged in this order in a direction from the measurement inlet35 toward the measurement outlet 36.

The branch measurement path 351 extends from the measurement inlet 35 inthe housing basal end direction, and is a portion of the measurementflow path 32 branched from the through flow path 31. The branchmeasurement path 351 forms the measurement inlet 35, and an upstream endof the branch measurement path 351 serves as the measurement inlet 35.The branch measurement path 351 is inclined with respect to both theheight direction Y and the depth direction Z. The branch measurementpath 351 is inclined with respect to the through flow path 31.

The introduction measurement path 352 extends from a downstream end ofthe branch measurement path 351 in a direction away from the throughflow path 31 along the height direction Y. The introduction measurementpath 352 guides air flowing from the branch measurement path 351 towardthe flow rate sensor 22.

The detection measurement path 353 extends in the depth direction Z froma downstream end of the introduction measurement path 352, and isprovided opposite the branch measurement path 351 via the introductionmeasurement path 352. The flow rate sensor 22 is provided in thedetection measurement path 353.

The discharge measurement path 354 extends from a downstream end of thedetection measurement path 353 toward the through flow path 31 in theheight direction Y, and is provided parallel to the introductionmeasurement path 352. The discharge measurement path 354 forms themeasurement outlet 36, and a downstream end of the discharge measurementpath 354 serves as the measurement outlet 36. In this case, thedischarge measurement path 354 discharges air flowing from the detectionmeasurement path 353 through the measurement outlet 36.

As shown in FIG. 41, the branch measurement path 351 includes a portionthat extends straight from the measurement inlet 35 toward theintroduction measurement path 352. A center line of this portion isdefined as a branch measurement line CL23. The branch measurement lineCL23 extends linearly and is inclined with respect to the inlet ceilingsurface 342. The branch measurement line CL23 extends obliquely from themeasurement inlet 35 toward a downstream side of the branch measurementpath 351 in a direction away from the through inlet 33. In other words,the branch measurement line CL23 extends obliquely from the measurementinlet 35 toward the downstream side of the branch measurement path 351in a direction toward the through outlet 34.

In FIG. 41, the inner surface of the housing 21 is chamfered at thebranch portion between the through flow path 31 and the measurement flowpath 32, but the branch measurement line CL23 is set assuming aconfiguration without this chamfered portion. The branch measurementline CL23 includes an extended line obtained by extending the centerline of the branch measurement path 351 from the measurement inlet 35toward the through flow path 31.

The branch measurement line CL23 is inclined with respect to the inletfloor surface 346. An inclination angle θ23 of the branch measurementline CL23 with respect to the inlet floor surface 346 is more than orequal to 90 degrees. That is, the inclination angle θ23 is a value sameas 90 degrees or a value larger than 90 degrees. There is arelationship: θ23≥90°. The inclination angle θ23 is between the floorparallel line CL21 and the branch measurement line CL23 facing thethrough inlet 33. In the range of θ23 which is 90 degrees or more, θ23is preferably 150 degrees or less, and more preferably 120 degrees orless.

The branch measurement line CL23 is inclined with respect to not onlythe inlet floor surface 346 but also the main flow line CL22. Aninclination angle θ24 of the branch measurement line CL23 with respectto the main flow line CL22 is more than or equal to 90 degrees, similarto the inclination angle θ23. That is, the inclination angle θ24 is avalue same as 90 degrees or a value larger than 90 degrees. There is arelationship: θ24≥90°. The inclination angle θ24 is between the mainflow line CL22 and the branch measurement line CL23 facing the throughinlet 33. The inclination angle θ24 is included in the obtuse angle. Inthe range of θ24 which is 90 degrees or more, θ24 is preferably 150degrees or less, and more preferably 120 degrees or less.

The inclination angles θ23, θ24 are included in the obtuse angle. Thebranch measurement line CL23 is inclined with respect to not only theinlet floor surface 346 and the main flow line CL22 but also the inletceiling surface 342. An inclination angle of the branch measurement lineCL23 with respect to the inlet ceiling surface 342 is more than or equalto 10 degrees, similar to the inclination angle θ21, θ22.

The branch measurement path 351 is inclined with respect to the inletthrough path 331. In this case, the branch measurement line CL23 that isthe center line of the branch measurement path 351 is inclined withrespect to the inlet through line CL24 that is the center line of theinlet through path 331. An inclination angle θ25 of the branchmeasurement line CL23 with respect to the inlet through line CL24 ismore than or equal to 90 degrees. That is, the inclination angle θ25 isa value same as 90 degrees or a value larger than 90 degrees. There is arelationship: θ25≥90°. The inclination angle θ25 is between the branchmeasurement line CL23 and the inlet through line CL24 facing the throughinlet 33. The inlet through line CL24 is a linear imaginary line thatpasses through the center CO21 of the through inlet 33 that is anupstream end of the inlet through path 331 and a center CO22 of adownstream end of the inlet through path 331.

The branch measurement path 351 is inclined with respect to the outletthrough path 332. In this case, the branch measurement line CL23 isinclined with respect to an outlet through line CL25 that is the centerline of the outlet through path 332. An inclination angle θ26 of thebranch measurement line CL23 with respect to the outlet through lineCL25 is less than or equal to 60 degrees. That is, the inclination angleθ26 is a value same as 60 degrees or a value smaller than 60 degrees.There is a relationship: θ26≤60°. For example, the inclination angle θ26is set to 60 degrees. The outlet through line CL25 is a linear imaginaryline that passes through a center CO23 of an upstream end of the outletthrough path 332 and the center CO24 of the through outlet 34 that is adownstream end of the outlet through path 332. The outlet through lineCL25 is inclined with respect to the inlet through line CL24.

The inclination angle θ26 of the branch measurement line CL23 withrespect to the outlet through line CL25 is an inclination angle of thebranch measurement path 351 with respect to the branch through path 333,and corresponds to a branch angle indicating an angle at which themeasurement flow path 32 branches from the through flow path 31.

Next, air flow in the bypass flow path 30 will be described withreference to FIGS. 43 to 46. The air flow through the intake passage 12includes main flows AF21, AF22 and deflected flows AF23 to AF26.

As shown in FIG. 43, the main flows AF21, AF22 travel through the intakepassage 12 along the main flow line CL22 in the main flow direction, andenter the inlet through path 331 from the through inlet 33 withoutchange in traveling direction. Among the main flows AF21, AF22, a mainflow AF21 enters the through inlet 33 near the inlet ceiling surface342, and travels toward the inlet ceiling surface 342. When approachingthe inlet ceiling surface 342, the main flow AF21 changes in travelingdirection by the inlet ceiling surface 342. In this case, the inletceiling surface 342 changes the traveling direction of the main flowAF21 into a direction toward the through floor surface 345. Thus, evenif a foreign matter such as dust enters the through inlet 33 togetherwith the main flow AF21, the foreign matter easily travels toward thethrough floor surface 345, and the foreign matter does not easily enterthe measurement inlet 35.

On the other hand, another main flow AF22 enters the through inlet 33near the inlet floor surface 346, and travels toward the through floorsurface 345 such as the inlet floor surface 346 or the branch floorsurface 348. When approaching the through floor surface 345, the mainflow AF22 changes in traveling direction by the through floor surface345. In this case, the through floor surface 345 changes the travelingdirection of the main flow AF22 into a direction toward the throughoutlet 34. Thus, even if the foreign matter enters the through inlet 33together with the main flow AF22, the foreign matter easily travelsalong the through floor surface 345 toward the through outlet 34, andthe foreign matter does not easily enter the measurement inlet 35.

As shown in FIGS. 44, 45, the deflected flows AF23 to AF26 travelthrough the intake passage 12 in directions inclined with respect to themain flow line CL22 and the main flow direction in the main flowdirection, and enter the inlet through path 331 from the through inlet33 without change in traveling direction.

As shown in FIG. 44, among the deflected flows AF23 to AF26, downwarddeflected flows AF23, AF24 are airflows that obliquely travel in theintake passage 12 around the housing 21 in the housing distal enddirection which is opposite from the housing basal end direction. Here,the downward deflected flows AF23, AF24 are defined as airflows whichare smaller than the inlet ceiling surface 342 in inclination angle withrespect to the main flow line CL22.

Among the downward deflected flows AF23, AF24, a downward deflected flowAF23 entering the through inlet 33 near the inlet ceiling surface 342easily travels toward the through floor surface 345 along the inletceiling surface 342. In particular, if the downward deflected flow AF23and the inlet ceiling surface 342 are substantially the same ininclination angle with respect to the main flow direction, the travelingdirection of the downward deflected flow AF23 is unlikely to change dueto the inlet ceiling surface 342. In these cases, even if a foreignmatter enters the through inlet 33 together with the downward deflectedflow AF23, the foreign matter easily travels toward the through floorsurface 345, and the foreign matter does not easily enter themeasurement inlet 35.

On the other hand, another downward deflected flow AF24 enters thethrough inlet 33 near the inlet floor surface 346, and travels towardthe through floor surface 345. When approaching the through floorsurface 345, the downward deflected flow AF24 changes in travelingdirection by the through floor surface 345. In this case, the throughfloor surface 345 changes the traveling direction of the downwarddeflected flow AF24 into a direction toward the through outlet 34. Inthis case, even if the foreign matter enters the through inlet 33together with the downward deflected flow AF24, the foreign mattereasily travels along the through floor surface 345 toward the throughoutlet 34, and the foreign matter does not easily enter the measurementinlet 35.

As shown in FIG. 45, among the deflected flows AF23 to AF26, upwarddeflected flows AF25, AF26 are airflows that obliquely travel in theintake passage 12 around the housing 21 in the housing basal enddirection which is opposite from the housing distal end direction. Here,the upward deflected flows AF25, AF26 are defined as airflows which arelarger than the inlet floor surface 346 in inclination angle withrespect to the main flow line CL22.

Among the upward deflected flows AF25, AF26, an upward deflected flowAF25 enters the through inlet 33 near the inlet ceiling surface 342, andtravels toward the inlet ceiling surface 342. When approaching the inletceiling surface 342, the upward deflected flow AF25 changes in travelingdirection by the inlet ceiling surface 342. In this case, the inletceiling surface 342 changes the traveling direction of the upwarddeflected flow AF25 into a direction toward the through floor surface345. Thus, even if a foreign matter such as dust enters the throughinlet 33 together with the upward deflected flow AF25, the foreignmatter easily travels toward the through floor surface 345, and theforeign matter does not easily enter the measurement inlet 35.

On the other hand, another upward deflected flow AF26 entering thethrough inlet 33 near the inlet floor surface 346 easily travels towardthe inlet ceiling surface 342 and the measurement inlet 35. That is, theupward deflected flow AF26 easily flows in a direction away from thethrough floor surface 345 such as the inlet floor surface 346 afterentering the inlet through path 331 from the through inlet 33. In thiscase, separation of the upward deflected flow AF26 from the throughfloor surface 345 causes a vortex AF27 that swirls toward the throughfloor surface 345, and thus turbulence of the upward deflected flow AF26is easily generated. When turbulence of the upward deflected flow AF26is generated in this way, the upward deflected flow AF25 near the inletceiling surface 342 is also disturbed by the turbulence of the upwarddeflected flow AF26, so that the air flow tends to be disturbedthroughout the through flow path 31. In this case, the turbulent airflowmay flow into the measurement flow path 32 from the measurement inlet35, which may reduce the accuracy in flow rate detection of the flowrate sensor 22.

However, since the upward deflected flow AF25, which has been changed intraveling direction by the inlet ceiling surface 342, is travelingtoward the through floor surface 345, the upward deflected flow AF25presses the upward deflected flow AF26 toward the through floor surface345. In this case, the upward deflected flow AF25 traveling toward thethrough floor surface 345 changes the traveling direction of the upwarddeflected flow AF26 near the inlet floor surface 346 into a directiontoward the through floor surface 345. Thus, the upward deflected flowAF26 is unlikely to be separated from the through floor surface 345, andas a result, the vortex AF27 that occurs in connection with theseparation is also unlikely to occur. Therefore, the turbulence of theair flow in the through flow path 31 due to generation of the vortexAF27 is suppressed.

In the air flow meter 20, a fluctuation mode of an output related to theflow rate measurement is correlated with the inclination angle θ21 ofthe inlet ceiling surface 342 with respect to the inlet floor surface346. Specifically, when a fluctuation in measured value of the air flowmeter 20 with respect to the true air flow rate in the intake passage 12is calculated as an output fluctuation, the output fluctuation isproperly managed in a configuration in which the inclination angle θ21of the inlet ceiling surface 342 with respect to the inlet floor surface346 is 10 degrees or more. For example, when the inclination angle θ21is in a range larger than 0 degree and smaller than 10 degrees, theoutput fluctuation of the air flow meter 20 becomes smaller as theinclination angle θ21 is closer to 10 degrees. When the inclinationangle θ21 is in a range lager than or equal to 10 degrees, the outputfluctuation of the air flow meter 20 is appropriately kept at a smallvalue. In the range of θ21 which is 10 degrees or more, θ21 ispreferably 60 degrees or less, and more preferably 30 degrees or less.

The output fluctuation of the air flow meter 20 is also correlated withthe inclination angle θ22 of the inlet ceiling surface 342 with respectto the main flow line CL22. This output fluctuation is properly managedby a configuration in which the inclination angle θ22 of the inletceiling surface 342 with respect to the main flow line CL22 is more thanor equal to 10 degrees. For example, as shown in FIG. 46, when theinclination angle θ22 is in a range larger than 0 degree and smallerthan 10 degrees, the output fluctuation of the air flow meter 20 becomessmaller as the inclination angle θ22 is closer to 10 degrees. When theinclination angle θ22 is in a range lager than or equal to 10 degrees,the output fluctuation of the air flow meter 20 is appropriately kept ata small value. In the range of θ22 which is 10 degrees or more, θ21 ispreferably 60 degrees or less, and more preferably 30 degrees or less.

In the intake passage 12 shown in FIG. 41, when pulsations occur in aflow of the intake air due to an operation state of the engine or thelike, not only a forward flow flowing from the upstream side but also abackward flow flowing from the downstream side in the opposite directionto the forward flow may occur in association with the pulsations. Whilethe forward flow flows into the through flow path 31 from the throughinlet 33, the backward flow may flow into the through flow path 31 fromthe through outlet 34. For example, when the forward flow flows inthrough the through inlet 33 and then flows into the measurement flowpath 32 from the through flow path 31, a flow rate of the forward flowis detected by the flow rate sensor 22. On the other hand, when thebackward flow generated in the intake passage 12 flows in through thethrough outlet 34 and then flows into the measurement flow path 32 fromthe through flow path 31, a flow rate of the backward flow is detectedby the flow rate sensor 22.

The flow rate sensor 22 can detect not only a flow rate of air in themeasurement flow path 32 but also a flow of the air in the measurementflow path 32. However, if the backward flow from the through outlet 34flows into the measurement flow path 32, the backward flow flows in themeasurement flow path 32 from the measurement inlet 35 to themeasurement outlet 36, as with the forward flow from the through inlet33. Thus, in the measurement flow path 32, a direction of the backwardflow from the through outlet 34 and a direction of the forward flow fromthe through inlet 33 are identical to each other. Therefore, the flowrate sensor 22 cannot distinguishes between the forward flow and thebackward flow. For that reason, the air flow meter 20 measures the flowrate of the air, on the assumption that all of the air flowing throughthe measurement flow path 32 is the forward flow, even though the airflowing through the measurement flow path 32 actually includes thebackward flow. As a result, there is a concern that the measurementaccuracy of the air flow meter 20 may be lowered.

Further, in the intake passage 12, the turbulence of the air flow suchas a vortex flow or stagnation may occur as the air passes around theair flow meter 20. For example, when the air flowing through the intakepassage 12 flows past the housing front surface 21 e or the housing backsurface 21 f as a forward flow, a turbulence of air flow may occur dueto mixing of an air flow in the main flow direction and an air flowalong the housing downstream surface 21 d. When the turbulence of airflow exists around the through outlet 34, such as a downstream side ofthe housing downstream surface 21 d, the backward flow generated in theintake passage 12 involves the turbulence and becomes unstable. There isa concern that the unstable backward flow enters the through flow path31 from the through outlet 34.

In the air flow meter 20, the branch measurement path 351 extends in adirection from the through flow path 31 toward the through outlet 34.Thus, even if the backward flow enters the through flow path 31 from thethrough outlet 34, the backward flow is less likely to flow into thebranch measurement path 351 from the through flow path 31. Inparticular, as described above, the inclination angle θ26 of the branchmeasurement line CL23 with respect to the outlet through line CL25 isless than or equal to 60 degrees. Hence, the backward flow is moredifficult to flow into the branch measurement path 351 from the throughflow path 31.

In the bypass flow path 30, as described above, the measurement inlet 35does not face to the through inlet 33. Thus, a dynamic pressure of theforward flow from the through inlet 33 is less likely to be applied tothe measurement inlet 35 and, a flow velocity of air in the measurementflow path 32 is likely to increase. In the above configuration, even ifforeign matters such as sand particle, dust, waterdrops, and oildroplets enter the through flow path 31 from the through inlet 33together with the forward flow, the foreign matters hardly enters thebranch measurement path 351 from the through flow path 31. In that case,the foreign matters reaching the flow rate sensor 22 in the measurementflow path 32 is less likely to break the flow rate sensor 22 or adhereto the flow rate sensor 22. Thus, deterioration in detection accuracy ofthe flow rate sensor 22 due to the foreign matters can be reduced.

An entire of the through outlet 34 and at least a part of the throughinlet 33 overlap in the depth direction Z which is the main flowdirection. In this configuration, in the intake passage 12, when foreignmatters are contained in a main flow flowing into the part of thethrough inlet 33 which overlaps the through outlet 34 in the depthdirection Z, the foreign matters travel straight together with the mainflow in the main flow direction and are discharged from the throughoutlet 34 to outside. Therefore, foreign matters are difficult to enterthe measurement inlet 35.

A state of pulsation generated in the intake passage 12 is defined as apulsation characteristic. The pulsation characteristic measured by theair flow meter 20 by use of the detection result of the flow rate sensor22 may include an error as compared with a pulsation characteristic ofpulsation actually generated in the intake passage 12. A case where anerror is included in the pulsation characteristic measured by the airflow meter 20 includes a case where the backward flow from the throughoutlet 34 enters the measurement flow path 32 from the through flow path31.

In this example, the flow rate measured by the air flow meter 20 isreferred to as a flow rate measurement value GA, an average value of theflow rate measurement values GA is referred to as a measurement averagevalue GAave, the actual flow rate of the intake air flowing through theintake passage 12 is referred to as an actual flow rate GB, and anaverage value of the actual flow rate GB is referred to as an actualaverage value GBave. As shown in FIG. 47, when the flow rate measurementvalue GA becomes smaller than the actual flow rate GB due to theinclusion of an error in the flow rate measurement value GA, themeasurement average value GAave also becomes smaller than the actualaverage value GBave.

The pulsation characteristics can be quantified by a value obtained bydividing a difference between the measurement average value GAave andthe actual average value GBave by the actual average value GBave. Inthis instance, a mathematical expression for calculating the pulsationcharacteristics is expressed as (GAave−GBave)/GBave. The value of thepulsation characteristic tends to increase as the amplitude of thepulsation increases. For example, when a value obtained by dividing adifference between the maximum value GBmax of the actual flow rate GBand the actual average value GBave by the actual average value GBave isreferred to as an amplitude ratio, as shown in FIG. 48, a numericalvalue of the pulsation characteristic increases as the amplitude ratioincreases. In particular, in a region where the amplitude ratio islarger than 1, the rate of increase of the pulsation characteristic withan increase in the amplitude ratio is large. In this example, as theamplitude ratio is larger, the amount of the backward flow from thethrough outlet 34 becomes larger. A mathematical expression forcalculating the amplitude ratio can be expressed as (GBmax−GBave)/GBave.

In the present embodiment, the inclination angle θ26 of the branchmeasurement line CL23 with respect to the main flow line CL22 is set to,for example, 60 degrees, but a value of the pulsation characteristic islikely to change in accordance with the inclination angle θ26. Forexample, as shown in FIG. 49, in the configuration in which theinclination angle θ26 is 30 degrees, 45 degrees, 60 degrees, or 90degrees, when the backward flow flows into the through flow path 31 fromthe through outlet 34, the backward flow is less likely to flow into themeasurement flow path 32 with the configuration in which the inclinationangle θ26 is 30 degrees, 45 degrees, or 60 degrees. On the other hand,in the configuration in which the inclination angle θ26 is 90 degrees,the backward flow is likely to flow into the measurement flow path 32.In this case, the detection accuracy of the pulsation characteristic bythe air flow meter 20 is likely to be lowered.

In the air flow meter 20, it is considered that the tendency of thebackward flow flowing into the measurement flow path 32 differsdepending on the inclination angle θ26, as a result of which thenumerical values of the pulsation characteristic differs from eachother. For example, as shown in FIG. 50, in the configuration in whichthe inclination angle θ26 is 60 degrees or less, the numerical value ofthe pulsation characteristic is a relatively small value. It isconsidered that this is attributable to a phenomenon that when theinclination angle θ26 is equal to or less than 60 degrees, the backwardflow is less likely to flow into the measurement flow path 32. On theother hand, in the configuration in which the inclination angle θ26 islarger than 60 degrees, the numerical value of the pulsationcharacteristic is relatively large. This is considered to beattributable to the phenomenon that when the inclination angle θ26 islarger than 60 degrees, the backward flow is likely to flow into themeasurement flow path 32. In addition, in the above configuration, thenumerical value of the pulsation characteristic increases as theinclination angle θ26 increases. This is considered to be attributableto the phenomenon that, in a range in which the inclination angle θ26 islarger than 60 degrees, as the inclination angle θ26 is larger, thebackward flow is likely to flow into the measurement flow path 32.

According to the present embodiment described above, the inlet ceilingsurface 342 is inclined with respect to the inlet floor surface 346. Inthis configuration, an air flowing into the inlet through path 331 fromthe through inlet 33, which flows near the inlet ceiling surface 342,such as the upward deflected flow AF25, is changed in travelingdirection by the inlet ceiling surface 342. Accordingly, the air easilyflows toward the inlet floor surface 346 along the inlet ceiling surface342. Therefore, even if an air such as the upward deflected flow AF26separates or almost separates from the inlet floor surface 346, theseparating air is pressed against the inlet floor surface 346 by the airsuch as the upward deflected flow AF25 traveling toward the inlet floorsurface 346 along the inlet ceiling surface 342. In this case,occurrence of turbulence such as vortex due to the separation of airfrom the inlet floor surface 346 is regulated by a fluid flowing alongthe inlet ceiling surface 342. As a result, the turbulence of air isless likely to occur in the inlet through path 331. Therefore, the flowrate detection accuracy of the flow rate sensor 22 can be increased, andas a result, the flow rate measurement accuracy of the air flow meter 20can be increased.

According to the present embodiment, the inclination angle θ21 of theinlet ceiling surface 342 with respect to the inlet floor surface 346 is10 degrees or more. In this configuration, the inclination angle θ21 isset to a relatively large value so that the air such as the upwarddeflected flow AF25 which has been changed in traveling direction by theinlet ceiling surface 342 travels toward the inlet floor surface 346,not toward the through outlet 34. Hence, compared with a configurationin which the inclination angle θ21 is set to, for example, a valuesmaller than 10 degrees, the air such as the upward deflected flow AF25which has been changed in traveling direction by the inlet ceilingsurface 342 can certainly reduce occurrence of air separation near theinlet floor surface 346.

According to the present embodiment, the inlet ceiling surface 342 isinclined with respect to the inlet floor surface 346 such that the inletceiling surface 342 faces the through inlet 33. In this configuration,air such as the main flow AF21 and the downward deflected flow AF23entering the through inlet 33 near the inlet ceiling surface 342 is lesslikely to separate from the inlet ceiling surface 342. Therefore,occurrence of turbulence such as vortex in the air entering the throughinlet 33 near the inlet ceiling surface 342 can be reduced.

For example, in a configuration in which the inlet ceiling surface 342is inclined with respect to the inlet floor surface 346 such that theinlet ceiling surface 342 faces to the through outlet 34, the main flowAF21 entering the through inlet 33 near the inlet ceiling surface 342 islikely to gradually separates from the inlet ceiling surface 342 in thetraveling direction toward the through outlet 34. In this case, aturbulence of air flow is likely to occur in the through flow path 31due to generation of vortex or the like by the main flow AF21.

According to the present embodiment, the inlet ceiling surface 342 isinclined with respect to the main flow direction in which the main flowline CL22 extends such that the inlet ceiling surface 342 faces thethrough inlet 33. In this configuration, when air such as the main flowAF21 flowing in the main flow direction enters the through inlet 33 nearthe inlet ceiling surface 342, the air can be guided toward the inletfloor surface 346 by the inlet ceiling surface 342. Therefore, even ifan air such as the main flow AF22 along the main flow direction entersthe through inlet 33 near the inlet floor surface 346 and separates oralmost separates from the inlet floor surface 346, the air can bepressed against the inlet floor surface 346 by air traveling toward theinlet floor surface 346 from the inlet ceiling surface 342. Therefore,occurrence of turbulence such as the vortex AF27 in the air flow aroundthe inlet floor surface 346 can be reduced.

According to the present embodiment, the inclination angle θ22 of theinlet ceiling surface 342 with respect to the main flow direction is 10degrees or more. In this configuration, the deflected flows thatobliquely travel around the housing 21 in the housing distal enddirection, which is opposite from the housing basal end direction,include as much as possible the downward deflected flows AF23, AF24which are smaller than the inlet ceiling surface 342 in inclinationangle with respect to the main flow line CL22. As a result, occurrenceof turbulence such as vortex in the air flow due to the deflected flowsof air entering the through inlet 33 near the inlet ceiling surface 342and being separated from the inlet ceiling surface 342 can be reduced.

In contrast to this, for example, in a configuration where theinclination angle θ22 of the inlet ceiling surface 342 with respect tothe main flow direction is smaller than 10 degrees, an inclination angleof the downward deflected flow that obliquely travels around the housing21 in the housing distal end direction, which is opposite from thehousing basal end direction, is likely to be larger than the inclinationangle θ22. Hence, occurrence of turbulence such as vortex in the airflow due to the deflected flows of air entering the through inlet 33near the inlet ceiling surface 342 and being separated from the inletceiling surface 342 is a concern.

According to the present embodiment, the main flow direction in whichthe main flow line CL22 extends is a direction in which the anglesetting surface 27 a of the housing 21 extends. Therefore, use of theangle setting surface 27 a at the time of setting an attaching angle ofthe housing 21 with respect to the piping unit 14 can provide attachmentof the housing 21 to the piping unit 14 in an appropriate directionaccording to a flow direction of ambient air in the intake passage 12.That is, the housing 21 can be attached to the piping unit 14 in adirection in which the inlet ceiling surface 342 can exert itsseparation reducing effect.

According to the present embodiment, the cross-sectional area S21 of theinlet through path 331 gradually decreases in a direction from thethrough inlet 33 toward the through outlet 34. In this configuration,the degree of narrowing of the inlet through path 331 increases inaccordance with traveling of air from the through inlet 33 through theinlet through path 331 toward the through outlet 34. Therefore, the airis easily regulated by the inner surface of the housing 21. Thus, theair such as the upward deflected flow AF25 which has been changed intraveling direction by the inlet ceiling surface 342 is more likely totravel toward the inlet floor surface 346 without spreading in thehousing front direction or the housing back direction than the inletfloor surface 346. Accordingly, air turbulence near the inlet floorsurface 346 can be reduced. Therefore, the inlet through path 331 can beformed into a shape that easily exhibits the separation reducing effectof the inlet ceiling surface 342.

According to the present embodiment, the inclination angle θ25 of thebranch measurement line CL23 with respect to the inlet through line CL24is 90 degrees or more. In this configuration, the air flowing from thethrough inlet 33 through the inlet through path 331 along the inletthrough line CL24 can be made to flow into the measurement flow path 32from the inlet through path 331 by obtuse and gentle change in travelingdirection of the air without the need of acute and sharp change.Therefore, when the air flowing through the through flow path 31 flowsinto the measurement flow path 32, occurrence of turbulence of air flowdue to a sharp change in traveling direction can be reduced.

According to the present embodiment, the inclination angle θ26 of thebranch measurement line CL23 with respect to the main flow line CL22 is60 degrees or less. In this configuration, since the branch angle of themeasurement flow path 32 with respect to the through flow path 31 is 60degrees or less, the air flowing from the through inlet 33 into theinlet through path 331 can be made to flow into the measurement flowpath 32 from the inlet through path 331 without the need of sharp changein traveling direction. Therefore, turbulence of the air flow is lesslikely to occur at the time of the air flowing into the measurement flowpath 32 from the through flow path 31.

Further, in this configuration, the backward flow from the throughoutlet 34 needs to sharply and acutely turn in order to flow into thebranch measurement path 351 from the through flow path 31. For thisreason, a phenomenon in which the backward flow does not easily flowinto the branch measurement path 351 easily occur, and the backward flowreaching the flow rate sensor 22 can be reduced. Occurrence ofmeasurement by the air flow meter 20, in which a flow rate is measuredas if the forward flow from the through inlet 33 reaches the flow ratesensor 22 though the backward flow from the through outlet 34 actuallyreaches the flow rate sensor 22, can be reduced. Therefore, an accuracyof the flow rate measurement of the intake air by the air flow meter 20can be improved.

Further, in this configuration, when the forward flow flows into thebranch measurement path 351 from the through flow path 31, the directionof the forward flow may gradually change into a direction toward thebranch measurement path 351. In this case, as described above, thebackward flow is less likely to flow into the branch measurement path351, while the forward flow is likely to flow into the branchmeasurement path 351. Accordingly, decrease in flow velocity of theforward flow flowing into the measurement flow path 32 can be reduced.Thus, the accuracy in flow rate detection of the forward flow from thethrough inlet 33 by the flow rate sensor 22 can be enhanced.

According to the present embodiment, the opening area of the throughoutlet 34 is smaller than the opening area of the through inlet 33.Thus, the backward flow generated in the intake passage 12 is lesslikely to flow into the through outlet 34. Therefore, the backward flowflowing into the branch measurement path 351 can be more surely reduced.

Other Embodiments

Although a plurality of embodiments according to the present disclosurehave been described above, the present disclosure is not construed asbeing limited to the above-mentioned embodiments, and can be applied tovarious embodiments and combinations within a scope not departing fromthe spirit of the present disclosure.

<Modification of Configuration Group A>

As a modification A1, the front peak 111 a and the back peak 112 a inthe measurement flow path 32 may not be arranged in the width directionX. For example, among the peaks 111 a, 112 a, only the front peak 111 amay be arranged on the center line CL5 of the heating resistor 71. Inthis case, the back peak 112 a may be arranged at a position displacedfrom the center line CL5 in at least one of the height direction Y andthe depth direction Z.

As a modification A2, the front peak 111 a of the front narrowed portion111 does not have to be arranged on the center line CL5 of the heatingresistor 71. For example, the front peak 111 a just have to be alignedwith a part of the heating resistor 71 in the width direction X and facea part of the heating resistor 71. Further, the front peak 111 a justhave to be aligned with a part of the membrane portion 62 in the widthdirection X and face a part of the membrane portion 62. Furthermore, thefront peak 111 a just have to be aligned with a part of the flow ratesensor 22 in the width direction X and face a part of the flow ratesensor 22.

As a modification A3, narrowed portions such as the front narrowedportion 111 and the back narrowed portion 112 may be provided on themeasurement ceiling surface 102 or the measurement floor surface 101 inthe measurement flow path 32. For example, in the measurement flow path32, the narrowed portion only has to be provided on at least one of themeasurement floor surface 101, the measurement ceiling surface 102, thefront measurement wall surface 103, and the back measurement wallsurface 104.

As a modification A4, a physical quantity sensor for detecting aphysical quantity different from the flow rate of the intake air may beprovided in the measurement flow path. Examples of the physical quantitysensor provided in the measurement flow path include a detection unitfor detecting a temperature, a detection unit for detecting a humidity,a detection unit for detecting a pressure, and the like in addition tothe flow rate sensor 22, 202. Those detection units may be mounted onthe sensor SA 50, 220 as the detection unit or may be provided ascomponents separated from the sensor SA 50, 220.

As a modification A5, the air flow meter 20, 200 does not need toinclude the through flow path 31, 211. That is, the bypass flow path 30,210 may not be branched. For example, the measurement inlet 35, 215 ofthe measurement flow path 32, 212 may be provided on the outer surfaceof the housing 21, 201. In this configuration, all of the air that hasflowed into the housing 21, 201 from the measurement inlet 35, 215 flowsout from the measurement outlet 36, 216.

<Modifications of Configuration Group B>

As a modification B1, the housing partition may be provided on thehousing container surface. For example, in the first embodiment, asshown in FIG. 51, the housing partition 131 is provided on the housingcontainer surface 136. In this configuration, the housing partition 131extends toward the SA container surface 146 of the sensor SA 50. Thecenter line CL11 of the housing partition 131 extends in a directionintersecting the height direction Y. The housing partition 131 does notextend in the directions X, Z orthogonal to the height direction Y, butextends obliquely from the housing container surface 136 in the housingbasal end direction. Therefore, the center line CL11 of the housingpartition 131 intersects the housing container surface 136 notorthogonally but obliquely.

In this modification, the housing partition 131 is provided on thehousing container surface 136. Therefore, by simply pushing the sensorSA 50 beyond the SA container space 150, the tip end of the housingpartition 131 can be deformed so as to be scraped at the external cornerbetween the housing step surface 137 and the housing container surface136. As a result, the housing partition 131 is easily made into contactwith the housing container surface 136. In FIG. 51, a portion of thehousing partition 131 which was scraped and deformed by the sensor SA 50is illustrated by a chain double-dashed line.

As a modification B2, the housing partition may be provided on thehousing step surface in the second embodiment as in the firstembodiment. For example, as shown in FIG. 52, the housing partition 271is provided on the housing step surface 277. In this configuration, thefirst intermediate hole 236 a of the first intermediate wall 236 isformed by an end surface of the first intermediate wall 236 rather thanthe tip end of the housing partition 271. In FIG. 52, a portion of thehousing partition 271 which was crushed by the sensor SA 220 isillustrated by a chain double-dashed line.

Further, as shown in FIG. 53, in the base member 291, the baseprotrusion 271 a is provided on a wall surface of the first baseprotrusion 295 that faces in the housing basal end direction. In thecover member 292, the cover protrusion 271 b is provided on a surface ofthe first cover protrusion 297 that faces in the housing basal enddirection.

As a modification B3, the housing partition may be provided on thehousing flow path surface in the first embodiment as in the secondembodiment. For example, the housing partition 131 is provided on thehousing flow path surface 135.

As a modification B4, a unit recess into which the housing partition isinserted may be provided on the detection unit. For example, as shown inFIG. 54, in the first embodiment, the SA step surface 147 of the sensorSA 50 is provided with a SA recess 161 as the unit recess. In thisconfiguration, when the sensor SA 50 is mounted on the first housingpart 151, the housing partition 131 is inserted into the SA recess 161.A recessing direction of the SA recess 161 from the SA step surface 147is the same as a protruding direction of the housing partition 131 fromthe housing step surface 137. That is, the center line of the SA recess161 coincides with the center line CL11 of the housing partition 131.

According to this configuration, the housing partition 131 and an innersurface of the SA recess 161 are easily brought into contact with eachother. More specifically, a depth of the SA recess 161 which is a recessdepth from the SA step surface 147 is smaller than a protrusion heightof the housing partition 131 from the housing step surface 137. In thiscase, the sensor SA 50 is inserted through the housing opening 151 a,and the housing partition 131 is inserted into the SA recess 161. Then,the sensor SA 50 is further pushed such that the housing partition 131contacts the inner surface of the SA recess 161 and is deformed viacrushing. As a result, the housing partition 131 is easily made intocontact with the inner surface of the SA recess 161.

Even if the housing partition 131 is not in contact with the innersurface of the SA recess 161, a gap between the outer surface of thehousing partition 131 and the inner surface of the SA recess 161 has acurved shape. Therefore, a foreign matter or air is unlikely to passthrough the gap. Therefore, in manufacturing the second housing part152, the fact that the housing partition 131 is inserted into the SArecess 161 can prevent the molten resin from entering the measurementflow path 32 through the gap between the first housing part 151 and thesensor SA 50.

As a modification B5, a gap between the housing and the detection unitmay be partitioned by a unit partition of the detection unit. Forexample, as shown in FIG. 55, in the second embodiment, the sensor SA220 as the detection unit includes a SA partition 302 as the unitpartition. The SA partition 302 is a protrusion provided on the outersurface of the sensor SA 220, and projects from the sensor SA 220 towardthe housing 201. A tip end of the SA partition 302 is in contact withthe inner surface of the housing 201. The SA partition 302 is betweenthe outer surface of the sensor SA 220 and the inner surface of thehousing 201 and separates the SA container space 290 from themeasurement flow path 212.

The SA partition 302 is provided on the SA flow path surface 285 of thesensor SA 220. The SA partition 302 is provided in a portion of the SAflow path surface 285 that faces the housing flow path surface 275 ofthe housing 201, and projects outward and toward the housing flow pathsurface 275 in a direction intersecting the height direction Y. A centerline CL14 of the SA partition 302 extends linearly in the direction X, Zorthogonal to the height direction Y. The SA partition 302, togetherwith the SA flow path surface 285, extends to make a loop around anouter circumference of the sensor SA 220. In this case, the SA partition302 has a portion extending in the width direction X and a portionextending in the depth direction Z. The SA partition 302 has asubstantially rectangular frame shape as a whole.

The SA partition 302 has a tapered shape, similar to the housingpartition 131 of the first embodiment. In the housing 201, an endsurface of the first intermediate wall 236 is a flat surface, and a tipend of the SA partition 302 is in contact with this flat surface.

In the manufacturing process of the air flow meter 200, when the sensorSA 220 is attached to the base member 291, as shown in FIG. 56, the SApartition 302 is deformed like deformation of the base protrusion 271 aof the first embodiment. Specifically, the sensor SA 220 is pushed intothe base member 291 through the base opening 291 a such that the tip endof the SA partition 302 is deformed via crushing or scraping by thefirst base protrusion 295 of the base member 291. Further, when thecover member 292 is attached to the base member 291, the SA partition302 is deformed like deformation of the cover protrusion 271 b of thefirst embodiment. Specifically, the cover member 292 is pressed againstthe sensor SA 220 and the base member 291 such that the tip end of theSA partition 302 is deformed via crushing by the first cover protrusion297 of the cover member 292. In these cases, the crushing or scraping ofthe tip end of the SA partition 302 newly generates a tip end surfacewhich is easily come into tight contact with the housing flow pathsurface 275 of the housing 201. Accordingly, a sealing performancebetween the SA partition 302 and the housing flow path surface 275 isimproved.

As a modification B6, as shown in FIG. 57, the SA partition 302 may beprovided on the SA step surface 287 of the sensor SA 220 in themodification B5. The SA partition 302 extends in the height direction Ytoward the housing step surface 277. A center line CL4 of the SApartition 302 extends in the height direction Y. The SA partition 302,together with the SA step surface 287, extends to make a loop around anouter circumference of the sensor SA 220.

In the manufacturing process of the air flow meter 200, when the sensorSA 220 is attached to the base member 291, as shown in FIG. 58, the SApartition 302 is deformed by the base member 291, the protrusion 295 ofthe base member 291 and the protrusion 297 of the cover members 292,like the above modification B5. As a result, a new end surface of the SApartition 302 is easily made into contact with the housing flow pathsurface 275.

As shown in FIG. 58, the SA partition 302 is provided at a positioncloser to the SA flow path surface 285 than to the SA container surface286 on the SA step surface 287. In this structure, the measurement flowpath 212 and the SA container space 290 are partitioned by the SApartition 302 at a position as close as possible to the measurement flowpath 212. Thus, a part of the gap between the housing 201 and the sensorSA 220 included in the measurement flow path 212 can be made as small aspossible. Therefore, since the SA partition 302 is provided at aposition as close as possible to the SA flow path surface 285, thedetection accuracy of the flow rate sensor 202 can be improved.

As shown in FIGS. 57, 58, in such configuration in which the SApartition 302 provided on the SA step surface 287 is in contact with thehousing step surface 277, both the SA step surface 287 and the housingstep surface 277 intersect the height direction Y and face each other inthe height direction Y. Therefore, when the sensor SA 220 is insertedinto the first intermediate hole 236 a of the first intermediate wall236, the SA partition 302 is engaged with the housing step surface 277.Therefore, the SA partition 302 can be brought into tight contact withthe housing step surface 277 by simply pushing the sensor SA 220 intothe housing 201 toward the measurement flow path 212.

As a modification B7, the modifications B4 and B5 may be combined, and ahousing recess may be provided on the housing into which the unitpartition is inserted. For example, as shown in FIG. 59, in the firstembodiment, the sensor SA 50 as the detection unit includes a SApartition 162 as the unit partition, and the housing 21 includes ahousing recess 163. In this configuration, the SA partition 162 is aprotrusion provided on the outer surface of the sensor SA 50, andprojects from the sensor SA 50 toward the housing 21. The SA partition162 is inserted into the housing recess 163.

The SA partition 162 is provided on the SA step surface 147 of thesensor SA 50. The SA partition 162 extends in the height direction Y,and a center line CL13 of the SA partition 162 extends linearly andinclined with respect to both the SA step surface 147 and the housingstep surface 137. The SA partition 162, together with the SA stepsurface 147, extends to make a loop around an outer circumference of thesensor SA 50. In this case, the SA partition 162 has a portion extendingin the width direction X and a portion extending in the depth directionZ. The SA partition 162 has a substantially rectangular frame shape as awhole. The SA partition 162 has a tapered shape, similar to the housingpartition 131 of the first embodiment.

The housing recess 163 is provided on the housing step surface 137. Arecessing direction of the housing recess 163 from the housing stepsurface 137 is the same as a protruding direction of the SA partition162 from the SA step surface 147. That is, the center line of thehousing recess 163 coincides with the center line CL13 of the SApartition 162.

The SA partition 162 is inserted into the housing recess 163. Accordingto this configuration, the SA partition 162 and an inner surface of thehousing recess 163 are easily brought into contact with each other.Specifically, a depth of the housing recess 163 is smaller than theprotrusion height of the SA partition 162. In this case, the sensor SA50 is inserted through the housing opening 151 a, and the SA partition162 is inserted into the housing recess 163. Then, the sensor SA 50 isfurther pushed such that the SA partition 162 contacts the inner surfaceof the housing recess 163 and is deformed via crushing. As a result, theSA partition 162 is easily made into contact with the inner surface ofthe housing recess 163. Even if the SA partition 162 is not in contactwith the inner surface of the housing recess 163, a gap between theouter surface of the SA partition 162 and the inner surface of thehousing recess 163 has a curved shape. Therefore, a foreign matter orair is unlikely to pass through the gap.

In FIG. 59, angles between the center line CL13 of the SA partition 162and the housing step surface 137 include a container angle θ14 facingthe SA container space 150 and a flow path angle θ13 facing themeasurement flow path 32. The container angle θ14 is larger than theflow path angle θ13. That is, there is a relationship of θ14>θ13.According to this configuration, when the tip end of the SA partition162 contacts the housing step surface 137, the tip end of the SApartition 162 is more likely to tilt or collapse toward the SA containerspace 150 than toward the measurement flow path 32. Therefore, even ifcrushed dust such as fragments is generated at the time of the SApartition 162 being crushed by the housing step surface 137, the crusheddust is unlikely to enter the measurement flow path 32.

As shown in FIG. 59, in such configuration in which the SA partition 162provided on the SA step surface 147 is in contact with the housing stepsurface 137, both the SA step surface 147 and the housing step surface137 intersect the height direction Y and face each other in the heightdirection Y. Therefore, when the sensor SA 50 is inserted into the firsthousing part 151, the SA partition 162 is engaged with the housing stepsurface 137. In this case, the SA partition 162 can be brought intotight contact with the housing step surface 137 by simply pushing thesensor SA 50 into the first housing part 151 toward the measurement flowpath 32.

As a modification B8, the position the housing partition provided on thehousing step surface may not be closer to the housing flow path surfacethan to the housing container surface. For example, in the secondembodiment, the housing partition 271 is arranged at a position on thehousing step surface 277 closer to the housing container surface 276than to the housing flow path surface 275. Further, on the housing stepsurface 137, the housing flow path surface 135 and the housing containersurface 136 may be the same in distance to the housing partition 131.

As a modification B9, the position the unit partition provided on theunit step surface may not be closer to the unit flow path surface thanto the unit container surface. For example, in the modification B6, theSA partition 302 is provided at a position closer to the SA containersurface 286 than to the SA flow path surface 285 on the SA step surface287. Further, on the SA step surface 287, the SA flow path surface 285and the SA container surface 286 may be the same in distance to the SApartition 302.

As a modification B10, the housing partition may be provided on multiplesurfaces selected from among the housing step surface, the housing flowpath surface, and the housing container surface. In this configuration,the housing partitions provided on the respective multiple surfaces maybe connected to one another or may be independent from one another. Forexample, in the first embodiment, the housing partitions 131 provided onthe housing step surface 137 and the housing flow path surface 135 arearranged in the height direction Y independently from each other.

As a modification B11, the unit partition may be provided on multiplesurfaces selected from among the unit step surface, the unit flow pathsurface, and the unit container surface. In this configuration, the unitpartitions provided on the respective multiple surfaces may be connectedto one another or may be independent from one another. For example, inthe modification B7, the SA partitions 162 provided on the SA stepsurface 147 and the SA flow path surface 145 are arranged in the heightdirection Y independently from each other.

As a modification B12, the housing partition and the unit partition maynot make a loop around the detection unit. For example, on the housingstep surface 137 of the first embodiment, a higher portion and a lowerportion in height position in the height direction Y are arranged in thecircumferential direction. In this configuration, the housing partition131 is provided only on the lower portion among the higher portion andthe lower portion. In this case, since the higher portion of the housingstep surface 137 and the housing partition 131 are in contact with theSA step surface 147, no gap is generated between the inner surface ofthe first housing part 151 and the sensor SA 50. The housing partition131 does not have an annular shape though the housing partition 131extends in the width direction X and the depth direction Z.

As a modification B13, the physical quantity measurement device may haveboth the housing partition and the unit partition. For example, thehousing partition and the unit partition are arranged in the heightdirection Y. In this configuration, the unit partition may be providedon a surface among the housing step surface, the housing flow pathsurface and the housing container surface, which does not face a surfaceon which the housing partition is provided. The unit partition may beprovided on a surface which faces the surface on which the housingpartition is provided. The housing partition and the unit partition maybe in contact with each other. In this configuration, the housingpartition and the unit partition are pressed against each other as thedetection unit is inserted into the housing. Thus, at least one of thehousing partition and the unit partition is easily deformed. In thiscase, since the housing partition and the unit partition easily comeinto tight contact with each other, the sealing property at the boundarybetween the measurement flow path and the container space is improved byboth the housing partition and the unit partition.

As a modification B14, a shape of the housing partition does not have tochange before and after the detection unit is attached to the housing aslong as the housing partition is in contact with the outer surface ofthe detection unit. Similarly, a shape of the unit partition does nothave to change before and after the detection unit is attached to thehousing as long as the unit partition is in contact with the innersurface of the housing.

As a modification B15, the direction in which the housing partitionextends from the inner surface of the housing is not limited to theabove embodiments. For example, in the first embodiment, the containerangle θ12 does not have to be larger than the flow path angle θ11.Similarly, the direction in which the unit partition portion extendsfrom the outer surface of the detection unit is not limited to the aboveembodiments. For example, in the modification B7, the container angleθ14 does not have to be larger than the flow path angle θ13.

As a modification B16, the housing partition and the unit partition maynot have the tapered shapes. For example, in the first embodiment, thehousing partition 131 may have a rectangular vertical cross section. Inthis case, the width of the housing partition 131 in the directions X, Zorthogonal to the height direction Y is the same at the base end and thetip of the housing partition 131.

As a modification B17, the container space may be a space in which a gassuch as air exists inside the housing. In this configuration, the sealperformance at the boundary between the container space and themeasurement flow path is improved by the housing partition and the unitpartition. Thus, air can be prevented from flowing back and forthbetween the container space and the measurement flow path. Therefore,deterioration in accuracy of flow rate detection by the flow rate sensorin the measurement flow path due to air leakage from the measurementflow path to the container space and air intrusion from the containerspace to the measurement flow path can be reduced.

<Modifications of Configuration Group C>

As a modification C1, the inlet floor surface does not have to face tothe through inlet. For example, in the third embodiment described above,as shown in FIG. 60, the inlet floor surface 346 faces to the throughoutlet 34. In this configuration, the inlet floor surface 346 isinclined with respect to the main flow line CL22, the outlet floorsurface 347, and the branch floor surface 348 such that the inlet floorsurface 346 faces in a direction away from the through inlet 33 alongthe depth direction Z. Further, the inlet floor surface 346 may extendparallel to the main flow line CL22 as shown in FIG. 61. Further, anentire of the through floor surface 345 may face to the through outlet34, or may extend parallel to the main flow line CL22 as shown in FIG.61. In either configuration, the inlet ceiling surface 342 only has tobe inclined with respect to the inlet floor surface 346.

As a modification C2, the measurement inlet does not have to face to thethrough outlet. For example, in the third embodiment, as shown in FIG.61, the measurement inlet 35 does not face to either the through inlet33 or the through outlet 34. The measurement inlet 35 extends parallelto the main flow line CL22 and faces the through floor surface 345. Inthis configuration, the through floor surface 345 extends parallel tothe main flow line CL22, while the outlet ceiling surface 343 isinclined with respect to the main flow line CL22. The outlet ceilingsurface 343 is inclined with respect to the outlet floor surface 347such that the outlet ceiling surface 343 faces to the through outlet 34.

As a modification C3, a part of the inlet ceiling surface may be aceiling inclined surface. For example, in the third embodiment, as shownin FIG. 62, the inlet ceiling surface 342 includes a ceiling inclinedsurface 342 a and a ceiling connecting surface 342 b. In thisconfiguration, the ceiling inclined surface 342 a extends from thethrough inlet 33 toward the through outlet 34 and is inclined withrespect to the inlet floor surface 346. The ceiling inclined surface 342a faces to the through inlet 33 and is inclined with respect to not onlythe inlet floor surface 346 but also the main flow line CL22. In thedepth direction Z, a length of the ceiling inclined surface 342 a issmaller than a length of the inlet floor surface 346. The ceilingconnecting surface 342 b connects a downstream end of the ceilinginclined surface 342 a and an upstream end of the measurement inlet 35in the depth direction Z. The ceiling connecting surface 342 b extendsparallel to the main flow line CL22 extending in the main flowdirection. In the depth direction Z, for example, the length of theceiling inclined surface 342 a is larger than a length of the ceilingconnecting surface 342 b.

In this modification, the ceiling inclined surface 342 a is a portioncorresponding to the inlet ceiling surface 342 of the third embodiment.Therefore, an inclination angle of the ceiling inclined surface 342 awith respect to the inlet floor surface 346 is the inclination angleθ21, and an inclination angle of the ceiling inclined surface 342 a withrespect to the main flow line CL22 is the inclination angle θ22.Further, in the height direction Y, a distance between the ceilinginclined surface 342 a and the inlet floor surface 346 is the distanceH21.

As a modification C4, in the third embodiment, the inclination angle θ21of the inlet ceiling surface 342 with respect to the inlet floor surface346 may be a value equal to or less than the inclination angle θ22 ofthe inlet ceiling surface 342 with respect to the main flow line CL22.For example, as in the modification C1, the inlet floor surface 346 isinclined with respect to the main flow line CL22 such that the inletfloor surface 346 faces to the through outlet 34.

As a modification C5, in the third embodiment, when the inclinationangle θ21 of the inlet ceiling surface 342 with respect to the inletfloor surface 346 is larger than or equal to 10 degrees, the inclinationangle θ22 of the inlet ceiling surface 342 with respect to the main flowline CL22 does not have to be larger than or equal to 10 degrees. Forexample, the inlet ceiling surface 342 faces to the through outlet 34.In this configuration, the inclination angle θ22 of the inlet ceilingsurface 342 with respect to the main flow line CL22 is smaller than 10degrees while the inclination angle θ21 of the inlet ceiling surface 342with respect to the inlet floor surface 346 is larger than 10 degrees.In this case, the inlet floor surface 346 is largely inclined withrespect to the main flow line CL22 such that the inlet floor surface 346faces to the through inlet 33.

As a modification C6, in the third embodiment, the inclination angle θ23of the branch measurement line CL23 with respect to the inlet floorsurface 346 may be a value equal to or larger than the inclination angleθ24 of the branch measurement line CL23 with respect to the main flowline CL22. For example, as in the modification C4, the inlet floorsurface 346 is inclined with respect to the main flow line CL22 suchthat the inlet floor surface 346 faces to the through outlet 34.

As a modification C7, in the third embodiment, the inclination angle θ21of the inlet ceiling surface 342 with respect to the inlet floor surface346 may be a value within a range larger than 0 degree and smaller than10 degrees. Further, the inclination angle θ22 of the inlet ceilingsurface 342 with respect to the main flow line CL22 may be a valuewithin a range larger than 0 degree and smaller than 10 degrees.

As a modification C8, in the third embodiment, the inclination angle θ23of the branch measurement line CL23 with respect to the inlet floorsurface 346 may be a value within a range larger than 0 degree andsmaller than 90 degrees. Further, the inclination angle θ24 of thebranch measurement line CL23 with respect to the main flow line CL22 maybe a value within a range larger than 0 degree and smaller than 90degrees.

As a modification C9, in the third embodiment, the inlet ceiling surface342 and the inlet floor surface 346 may be curved so as to bulge orrecess in the housing distal end direction. In this configuration, forexample, a straight imaginary line passing through an upstream end and adownstream end of the inlet ceiling surface 342 is assumed. Aninclination of this imaginary line with respect to the inlet floorsurface 346 and the main flow line CL22 is used as the inclination ofthe inlet ceiling surface 342. On the other hand, a straight imaginaryline passing through an upstream end and a downstream end of the inletfloor surface 346 is assumed. An inclination of this imaginary line withrespect to the inlet ceiling surface 342 and the branch measurement lineCL23 is used as the inclination of the inlet floor surface 346.

As a modification C10, in the third embodiment, the through flow path 31need not have the outlet through path 332 as long as the through flowpath 31 has the inlet through path 331 and the branch through path 333.In this configuration, the downstream end of the branch through path 333serves as the through outlet 34. Further, in this configuration, thethrough ceiling surface 341 has the inlet ceiling surface 342, but doesnot have the outlet ceiling surface 343. Further, in this configuration,the through floor surface 345 has the inlet floor surface 346 and thebranch floor surface 348, but does not have the outlet floor surface347.

As a modification C11, in the third embodiment, the decrease rate of thecross-sectional area S21 of the inlet through path 331 between theupstream end and the downstream end of the inlet through path 331 maynot be a constant value. For example, the decrease rate of thecross-sectional area S21 decreases gradually in a direction from thethrough inlet 33 toward the through outlet 34. In this configuration, agraph showing the value of the cross-sectional area S21 in the inletthrough path 331 has a shape convex downward unlike FIG. 42.Alternatively, the decrease rate of the cross-sectional area S21increases gradually in the direction from the through inlet 33 towardthe through outlet 34. In this configuration, a graph showing the valueof the cross-sectional area S21 in the inlet through path 331 has ashape convex upward unlike FIG. 42.

As a modification C12, in the third embodiment, the cross-sectional areaS21 of the inlet through path 331 may not be the cross-sectional areaalong the direction orthogonal to the main flow line CL22, but across-sectional area along a direction orthogonal to the inlet throughline CL24.

As a modification C13, in the third embodiment, the branch measurementpath 351 may not extend straight from the measurement inlet 35 but maybe curved. In other words, the center line of the branch measurementpath 351 may be curved without extending straight. Regarding theconfiguration in which the center line of the branch measurement path351 is curved, a tangent line to the center line of the branchmeasurement path 351 at the measurement inlet 35 is defined as thebranch measurement line CL23.

As a modification C14, in the third embodiment, the inclination angleθ26 of the branch measurement line CL23 with respect to the outletthrough line CL25 may be a value within a range larger than 0 degree andsmaller than 60 degrees.

As a modification C15, in the measurement flow path 32, the flow ratesensor 22 may be provided in the branch measurement path 351, theintroduction measurement path 352, or the discharge measurement path354.

As a modification C16, in the air flow meter 20, the portion having theangle setting surface 27 a for setting the installation angle of thehousing 21 with respect to the intake passage 12 may not be the flange27. For example, the housing 21 is fixed to the pipe flange 14 c withbolts or the like in a state in which a part of the housing 21 is hookedon an end surface of the pipe flange 14 c of the piping unit 14. In thisconfiguration, a surface of the housing 21 that overlaps the end surfaceof the pipe flange 14 c is the angle setting surface. Since the anglesetting surface overlaps the end surface of the pipe flange 14 c, theinstallation angle of the housing 21 with respect to the intake passage12 is set.

<Modification of Configuration Group D>

As a modification D1, the downstream outer curved surface 421 may havean arched portion. As shown in FIG. 63, for example, the downstreamouter curved surface 421 includes a downstream outer arched surface 461in addition to the downstream outer horizontal surface 422 and thedownstream outer vertical surface 423. The downstream outer archedsurface 461 concavely extends along the center line CL4 of themeasurement flow path 32. The downstream outer arched surface 461 isarched so as to be continuously curved along the center line CL4. Thedownstream outer arched surface 461 is provided between the downstreamouter horizontal surface 422 and the downstream outer vertical surface423 in the direction in which the center line CL4 extends. Thedownstream outer arched surface 461 connects the downstream outerhorizontal surface 422 and the downstream outer vertical surface 423.

A radius of curvature R34 of the downstream outer arched surface 461 issmaller than the radius of curvature R33 of the upstream outer curvedsurface 411. Thus, similar to the first embodiment, the curve of thedownstream outer curved surface 421 is sharper than the curve of theupstream outer curved surface 411. On the other hand, the radius ofcurvature R34 of the downstream outer arched surface 461 is larger thanthe radius of curvature R32 of the downstream inner curved surface 425.Thus, the curve of the downstream outer curved surface 421 is gentlerthan the curve of the downstream inner curved surface 425.

The arrangement line CL31 passes through the downstream outer archedsurface 461 of the downstream outer curved surface 421 without throughthe downstream outer vertical surface 423. In this configuration, airthat has passed through the flow rate sensor 22 and traveled along thearrangement line CL31 changes its flow direction by hitting thedownstream outer arched surface 461. Thus, the air is easier to traveltoward the downstream side of the downstream curved path 407.

According to the present modification, the downstream outer curvedsurface 421 includes the downstream outer arched surface 461. Hence, theair blown out from between the sensor support 51 and the narrowedportions 111, 112 toward the downstream curved path 407 is likely toflow along the downstream outer arched surface 461. In this case, theair that has passed through the flow rate sensor 22 is less likely tostay in the downstream curved path 407. Therefore, decrease in the flowrate and flow velocity of the air passing through the flow rate sensor22 can be reduced.

Further, it is preferable that the radius of curvature R34 of thedownstream outer arched surface 461 is smaller than the radius ofcurvature R33 of the upstream outer curved surface 411 such that thedegree of recess of the downstream outer curved surface 421 is largerthan the degree of recess of the upstream outer curved surface 411. Inthis configuration, while the degree of recess of the downstream outercurved surface 421 is made as large as possible, the air reaching thedownstream curved path 407 from the flow rate sensor 22 easily flowstoward the measurement outlet 36 along an arch of the downstream outerarched surface 461. Therefore, increase in pressure loss in thedownstream curved path 407 due to air disruption in the downstreamcurved path 407 can be reduced by the shape of the downstream outercurved surface 421.

As a modification D2, in the modification D1, the downstream outercurved surface 421 includes the downstream outer arched surface 461, butmay not include at least one of the downstream outer horizontal surface422 and the downstream outer vertical surface 423. For example, thedownstream outer curved surface 421 does not include both the downstreamouter horizontal surface 422 and the downstream outer vertical surface423. In this configuration, the downstream outer arched surface 461connects the upstream end part and the downstream end part of thedownstream curved path 407. In this case, the downstream outer curvedsurface 421 is the downstream outer arched surface 461 as a whole. Thedownstream outer curved surface 421 corresponds to a downstream outerarched surface.

As a modification D3, the upstream outer curved surface 411 may includeat least one of an upstream outer vertical surface and an upstream outerhorizontal surface. The upstream outer vertical surface extends straightfrom the upstream end part of the upstream curved path 406. The upstreamouter horizontal surface extends straight from the downstream end partof the upstream curved path 406. In this configuration, the entire ofthe upstream outer curved surface 411 is not an upstream outer archedsurface. The upstream outer curved surface 411 includes not only the atleast one of the upstream outer vertical surface and the upstream outerhorizontal surface but also the upstream outer arched surface. Forexample, in a configuration in which the upstream outer curved surface411 includes the upstream outer vertical surface and the upstream outerarched surface, the arrangement line CL31 may pass through the upstreamouter vertical surface. Further, in the upstream outer curved surface411, an upstream outer internal corner may be formed as an internalcorner in which the upstream outer vertical surface and the upstreamouter horizontal surface join inwardly with each other.

As a modification D4, the upstream inner curved surface 415 may includeat least one of an upstream inner vertical surface and an upstream innerhorizontal surface. The upstream inner vertical surface extends straightfrom the upstream end part of the upstream curved path 406. The upstreaminner horizontal surface extends straight from the downstream end partof the upstream curved path 406. In this configuration, the entire ofthe upstream inner curved surface 415 is not an upstream inner archedsurface. The upstream inner curved surface 415 includes not only the atleast one of the upstream inner vertical surface and the upstream innerhorizontal surface but also the upstream inner arched surface. Further,in the upstream inner curved surface 415, an upstream outer externalcorner may be formed as an external corner in which the upstream innervertical surface and the upstream inner horizontal surface joinoutwardly.

As a modification D5, the downstream inner curved surface 425 mayinclude at least one of a downstream inner vertical surface and adownstream inner horizontal surface. The downstream inner verticalsurface extends straight from the downstream end part of the downstreamcurved path 407. The downstream inner horizontal surface extendsstraight from the downstream end part of the upstream curved path 407.In this configuration, the entire of the downstream inner curved surface425 is not a downstream inner arched surface. The downstream innercurved surface 425 includes not only the at least one of the downstreaminner vertical surface and the downstream inner horizontal surface butalso the downstream inner arched surface. Further, in the downstreaminner curved surface 425, a downstream outer external corner may beformed as an external corner in which the downstream inner verticalsurface and the downstream inner horizontal surface join outwardly.

As a modification D6, the outer curved surfaces 411, 421 and the innercurved surfaces 415, 425 may have at least one inclined surface inclinedwith respect to the arrangement line CL31, and thus may be curved notcontinuously but stepwise. For example, the downstream outer curvedsurface 421 has a downstream outer inclined surface as the inclinedsurface that extends straight in a direction inclined with respect tothe arrangement line CL31. In this configuration, a connection portionbetween the downstream outer horizontal surface 422 and the downstreamouter vertical surface 423 is chamfered by the downstream outer inclinedsurface. The downstream outer curved surface 421 does not have thedownstream outer internal corner 424. In addition, multiple downstreamouter inclined surfaces may be arranged along the center line CL4 of themeasurement flow path 32. In this configuration, the downstream outercurved surface 421 has a shape that is curved stepwise by the multipledownstream outer inclined surfaces.

As a modification D7, the configuration in which the degree of recess ofthe downstream outer curved surface 421 is larger than the degree ofrecess of the upstream outer curved surface 411 may be realizedregardless of the radius of curvature. For example, the entire of thedownstream outer curved surface 421 may be the downstream outer archedsurface. The entire of the upstream outer curved surface 411 may be theupstream outer arched surface. The radius of curvature R34 of thedownstream outer curved surface 421 may be greater than the radius ofcurvature R33 of the upstream outer curved surface 411. Also in thisconfiguration, as long as the length of the downstream outer curvedsurface 421 is smaller than the length of the upstream outer curvedsurface 411 in the direction in which the center line CL4 of themeasurement flow path 32 extends, the degree of recess of the downstreamouter curved surface 421 is larger than the degree of recess of theupstream outer curved surface 411.

As a modification D8, in the sensor path 405, at least the measurementfloor surface 101 only have to extend straight along the arrangementline CL31. Further, an upstream end part of the flow rate sensor 22 maybe provided at the upstream end part of the sensor path 405. Adownstream end part of the flow rate sensor 22 may be provided at thedownstream end part of the sensor path 405. For example, the length ofthe sensor path 405 and the length of the flow rate sensor 22 may be thesame in the depth direction Z.

As a modification D9, in the depth direction Z, the downstream end partof the upstream outer curved surface 411 may be provided at a positioncloser to the flow rate sensor 22 than the downstream end part of theupstream inner curved surface 415 is. In this case, the upstream endpart of the sensor path 405 is defined by the downstream end part of theupstream outer curved surface 411, not by the downstream end part of theupstream inner curved surface 415. Further, in the depth direction Z,the upstream end part of the downstream outer curved surface 421 may beprovided at a position closer to the flow rate sensor 22 than theupstream end part of the downstream inner curved surface 425 is. In thiscase, the downstream end part of the sensor path 405 is defined by theupstream end part of the downstream outer curved surface 421, not by theupstream end part of the downstream inner curved surface 425.

As a modification D10, the arrangement line CL31 only have to passthrough the flow rate sensor 22. The arrangement line CL31 does not haveto pass through the center CO1 of the heating resistor 71, for example,as long as the arrangement line CL1 passes through a part of the heatingresistor 71. Further, the arrangement line CL31 may pass through thecenter or a part of the membrane portion 62, and may pass through thecenter or a part of the flow rate sensor 22. Furthermore, thearrangement line CL31 may be inclined with respect to the angle settingsurface 27 a of the housing 21, the depth direction Z, or the main flowdirection as long as the arrangement line CL31 extends in the directionin which the upstream curved path 406 and the downstream curved path 407are arranged.

As a modification D11, if the flow rate sensor 22 is arranged closer tothe upstream outer curved surface 411 than to the downstream outercurved surface 421 on the arrangement line CL31, the sensor support 51does not need to be located at a position closer to the upstream outercurved surface 411 than to the downstream outer curved surface 421. Inthis case, in the sensor support 51, the flow rate sensor 22 is arrangedat a position closer to the molded upstream surface 55 c than to themolded downstream surface 55 d on the arrangement line CL31.

As a modification D12, if the flow rate sensor 22 is arranged closer tothe upstream outer curved surface 411 than to the downstream outercurved surface 421 on the arrangement line CL31, the flow rate sensor 22does not need to be located at a position closer to the upstream endpart of the sensor path 405 than to the downstream end part of thesensor path 405. In this case, on the arrangement line CL31, a distancebetween the upstream end part of the downstream curved path 407 and thedownstream outer curved surface 421 is larger than a distance betweenthe downstream end part of the upstream curved path 406 and the upstreamouter curved surface 411.

As a modification D13, in the measurement flow path 32, the upstreamcurved path 406 and the downstream curved path 407 may be curved inopposite directions with respect to the sensor path 405. For example,both the upstream curved path 406 and the downstream curved path 407 maynot extend from the sensor path 405 in the housing distal end direction.One of them may extend in the housing distal end direction, and anotherof them may extend in the housing basal end direction. If the upstreamcurved path 406 extends from the sensor path 405 in the housing distalend direction, and the downstream curved path 407 extends from thesensor path 405 in the housing basal end direction, the downstream outercurved surface 421 extends from the measurement ceiling surface 102without extending from the measurement floor surface 101. Further, thedownstream inner curved surface 425 extends from the measurement floorsurface 101 without extending from the measurement ceiling surface 102.

As a modification D14, the measurement narrowing surface and themeasurement expanding surface of the measurement narrowed portion may bearched so as to be recessed, or may extend straight without beingarched. For example, as shown in FIG. 64, in the narrowed portions 111,112, the narrowing surfaces 431, 441 extend straight from the peaks 111a, 112 a to upstream, and the expanding surfaces 432, 442 extendstraight from the peaks 111 a, 112 a to downstream. The narrowingsurfaces 431, 441 are inclined with respect to the arrangement line CL31so as to face upstream in the measurement flow path 32. The expandingsurfaces 432, 442 are inclined with respect to the arrangement line CL31so as to face downstream in the measurement flow path 32. Increase ratesof the protrusion heights of the narrowing surfaces 431, 441 areconstant from the narrowing upstream surfaces 433, 443 toward the peaks111 a, 112 a. Decrease rates of the protrusion heights of the expandingsurfaces 432, 442 are constant from the peaks 111 a, 112 a toward theexpanding downstream surfaces 434, 444.

The narrowed portions 111, 112 have end surfaces extending along thearrangement line CL1, and these end surfaces are the peaks 111 a, 112 a.The centers of the peaks 111 a, 112 a in the depth direction Z are atpositions closer to the downstream curved path 407 than the center lineCL5 of the heating resistor 71 is.

According to this modification, since the front narrowing surface 431and the back narrowing surface 441 extend straight. Therefore, the airflow regulating effect by these narrowing surfaces 431, 441 can beimproved. Further, the front expanding surface 432 and the backexpanding surface 442 extend straight. Therefore, turbulence of airflowsuch as separation of the airflow from the expanding surfaces 432, 442is likely to be generated without deteriorating the detection accuracyof the flow rate sensor 22. In this case, the velocity energy of the airblown out as a jet flow toward the downstream curved path 407 frombetween the sensor support 51 and the expanding surfaces 432, 442 can bereduced. Therefore, it can be reduced that the jet flow bounces back onthe downstream outer curved surface 421 and returns to the flow ratesensor 22 as a backward flow.

In the measurement narrowed portion, only one of the measurementnarrowing surface and the measurement expanding surface may extendstraight. Specifically, at least one of the front narrowing surface 431,the front expanding surface 432, the back narrowing surface 441, and theback expanding surface 442 may extend straight. Further, the front peak111 a and the back peak 112 a may be convexly arched or may be concavelyarched.

As a modification D15, the shapes and sizes of the narrowed portions111, 112 may be different from the configuration of the firstembodiment. For example, in the narrowed portions 111, 112, the lengthW32 a, W32 b of the narrowing surfaces 431, 441 are not need to besmaller than the lengths W33 a, W33 b of the expanding surfaces 432,442. Further, the front narrowing upstream surface 433 and the frontexpanding downstream surface 434 may not be coplanar with each other. Inthis case, the protrusion height of the front narrowing surface 431 fromthe front narrowing upstream surface 433 is different from theprotrusion height of the front expanding surface 432 from the frontexpanding downstream surface 434. Also in the back narrowed portion 112,as in the front narrowed portion 111, the back narrowing upstreamsurface 443 and the back expanding downstream surface 444 may not becoplanar with each other. In this case, the protrusion height of theback narrowing surface 441 from the back narrowing upstream surface 443is different from the protrusion height of the back expanding surface442 from the back expanding downstream surface 444.

As a modification D16, the front narrowed portion 111 and the backnarrowed portion 112 may have different shapes and sizes. For example,the length W31 a of the front narrowed portion 111 may be larger orsmaller than the length W31 b of the back narrowed portion 112. Thelength W32 a of the front narrowing surface 431 may be larger or smallerthan the length W32 b of the back narrowing surface 441. The length W33a of the front expanding surface 432 may be larger or smaller than thelength W33 b of the back expanding surface 442. The protrusion heightD32 a, D36 a of the front peak 111 a may be the same as or smaller thanthe protrusion height D32 b, D36 b of the back peak 112 a.

As a modification D17, the narrowed portions 111, 112 may extend outwardof the measurement partition 451 in the depth direction Z. Further, thenarrowed portions 111 and 112 may be positioned so as not enter aninside of the upstream curved path 406 or an inside of the downstreamcurved path 407. For example, the narrowed portions 111, 112 may beprovided only in the sensor path 405 among the sensor path 405, theupstream curved path 406, and the downstream curved path 407. Furtherthe narrowed portions 111, 112 may not be bridged by the measurementceiling surface 102 and the measurement floor surface 101. For example,the narrowed portions 111 and 112 may extend from only one of themeasurement ceiling surface 102 and the measurement floor surface 101.Further, the narrowed portions 111, 112 may be provided between themeasurement ceiling surface 102 and the measurement floor surface 101but apart from both the measurement ceiling surface 102 and themeasurement floor surface 101.

As a modification D18, the measurement narrowed portions such as thenarrowed portions 111 and 112 only have to be provided on at least oneof the front measurement wall surface 103, the back measurement wallsurface 104, the outer measurement curved surface 401, and the innermeasurement curved surface 402 in the measurement flow path 32. Forexample, at least one of the front narrowed portion 111 and the backnarrowed portion 112 is provided. Further, the measurement narrowedportions may be provided to each of the measurement wall surfaces 103,104 and the measurement curved surface 401, 402.

As a modification D19, the degree of bulge of the downstream innercurved surface 425 may not be smaller than the degree of bulge of theupstream inner curved surface 415. Further, the degree of recess of thedownstream outer curved surface 421 may be smaller than the degree ofbulge of the downstream inner curved surface 425. Moreover, the degreeof recess of the upstream outer curved surface 411 may be larger thanthe degree of bulge of the upstream inner curved surface 415. In anyconfiguration, it is preferable that there is a relationship: L35 b>L35a in the measurement flow path 32.

As a modification D20, there may not be the relationship: L35 b>L35 a inthe measurement flow path 32. That is, the distance L35 b between thedownstream outer curved surface 421 and the downstream inner curvedsurface 425 may not be larger than the distance L35 a between theupstream outer curved surface 411 and the upstream inner curved surface415.

As a modification D21, the degree of recess of the downstream outercurved surface 421 does not have to be larger than the degree of recessof the upstream outer curved surface 411.

As a modification D22, the flow rate sensor 22 may not be arrangedcloser to the upstream outer curved surface 411 than to the downstreamouter curved surface 421 on the arrangement line CL31.

<Modifications of Configuration Group E>

As a modification E1, a portion of the molded upstream surface 55 c ofthe sensor support 51, which is provided in the measurement flow path32, may be entirely arranged upstream of the narrowed portions 111, 112.That is, in the measurement flow path 32, as long as the portion of themolded upstream surface 55 c included in the arrangement cross sectionCS41 is provided upstream of the narrowed portions 111, 112, the otherportions may not be provided upstream of the narrowed portions 111, 112.

As a modification E2, in the arrangement cross section CS41, the moldedupstream surface 55 c may be arranged upstream of at least one of thefront narrowed portion 111 and the back narrowed portion 112. Forexample, the back narrowed portion 112 is arranged downstream of themolded upstream surface 55 c in the arrangement cross section CS41.

As a modification E3, in the sensor support 51, the molded upstreaminclined surface 471 may be inclined with respect to the heightdirection Y such that the molded upstream inclined surface 471 graduallyapproach the molded downstream surface 55 d in a direction toward themolded basal end surface 55 b. Further, the molded upstream inclinedsurface 471 may be a curved surface such as an arched surface that iscurved so as to convex or concave in the depth direction Z.

As modification E4, the molded upstream surface 55 c of the sensorsupport 51 may not have the molded upstream inclined surface 471. Forexample, the molded upstream surface 55 c is not inclined with respectto the height direction Y and extends from the molded distal end surface55 a toward the molded basal end surface 55 b.

As a modification E5, at least a part of the molded upstream surface 55c of the sensor support 51 may be provided in the upstream curved path406. For example, the entire molded upstream inclined surface 471 isprovided in the upstream curved path 406. Further, the sensor support 51may be provided at a position away from the upstream curved path 406.

As a modification E6, a portion of the molded downstream surface 55 d ofthe sensor support 51, which is provided in the measurement flow path32, may be entirely arranged upstream of the downstream ends 111 c, 112c of the narrowed portions 111, 112. That is, in the measurement flowpath 32, as long as the portion of the molded downstream surface 55 dincluded in the arrangement cross section CS41 is provided upstream ofthe downstream ends 111 c, 112 c of the narrowed portions 111, 112, theother portions may not be provided upstream of the downstream ends 111c, 112 c.

As a modification E7, in the arrangement cross section CS41, the moldeddownstream surface 55 d may be arranged upstream of at least one of thefront downstream end 111 c of the front narrowed portion 111 and theback downstream end 112 c of the back narrowed portion 112. For example,the back downstream end 112 c of the back narrowed portion 112 isarranged downstream of the molded downstream surface 55 d in thearrangement cross section CS41.

As a modification E8, in the sensor support 51, the molded downstreaminclined surface 472 may be inclined with respect to the heightdirection Y such that the molded downstream inclined surface 472gradually approach the molded upstream surface 55 c in a directiontoward the molded basal end surface 55 b. Further, the molded downstreaminclined surface 472 may be a curved surface such as an arched surfacethat is curved so as to convex or concave in the depth direction Z.

As modification E9, the molded downstream surface 55 d of the sensorsupport 51 may not have the molded downstream inclined surface 472. Forexample, the molded downstream surface 55 d is not inclined with respectto the height direction Y and extends from the molded distal end surface55 a toward the molded basal end surface 55 b.

As a modification E10, at least a part of the molded downstream surface55 d of the sensor support 51 may be provided in the downstream curvedpath 407. For example, the entire molded downstream inclined surface 472is provided in the downstream curved path 407. Further, the sensorsupport 51 may be provided at a position away from the downstream curvedpath 407.

As a modification E11, a portion of the molded downstream surface 55 dof the sensor support 51, which is provided in the measurement flow path32, may be entirely arranged downstream of the narrowed portions 111,112.

As a modification E12, the flow rate sensor 22 may be provideddownstream or upstream of the front peak 111 a or the back peak 112 a,as long as the flow rate sensor 22 is disposed at a position where theflow velocity is the highest in the measurement flow path 32. Further,the flow rate sensor 22 may be provided at a position different from theposition where the flow velocity is the highest in the measurement flowpath 32.

As a modification E13, the opening area of the measurement outlet 36 maynot be smaller than the opening area of the measurement inlet 35.Further, the opening area of the through outlet 34 may not be smallerthan the opening area of the through inlet 33.

<Features of Configuration Group A>

The configurations disclosed in the present specification include thefeatures of the configuration group A as described below.

[Feature A1]

A physical quantity measurement device (20) for measuring a physicalquantity of a fluid, the physical quantity measurement devicecomprising:

a measurement flow path (32) through which the fluid flows;

a housing (21) forming the measurement flow path; and

a detection unit (50) including a physical quantity sensor (22) thatdetects the physical quantity of the fluid in the measurement flow path,and a sensor support (51) that has a plate shape and supports thephysical quantity sensor, the detection unit being attached to thehousing such that a support end (55 a) that is an end of the sensorsupport and the physical quantity sensor are housed in the measurementflow path, wherein

the sensor support includes:

-   -   a support front surface (55 e) which is one plate surface of the        sensor support on which the physical quantity sensor is        disposed; and    -   a support back surface (55 f) behind the support front surface,

the housing includes forming surfaces that form the measurement flowpath, and the forming surfaces include:

-   -   a floor surface (101) facing the support end;    -   a front wall surface (103) facing the support front surface; and    -   a back wall surface (104) opposite to the front wall surface        across the floor surface and facing the support back surface,

a front distance (L1) is a distance between the physical quantity sensorand the front wall surface in a front-back direction (X) in which thefront wall surface and the back wall surface are arranged,

a floor distance (L3) is a distance between the floor surface and thesupport end in a height direction (Y) in which the floor surface and thesupport are arranged, the height direction being orthogonal to thefront-back direction, and

the front distance is larger than the floor distance.

[Feature A2]

The physical quantity measurement device according to Feature A1,wherein the front distance is smaller than a back distance (L2) which isa distance between the back wall surface and the support back surface inthe front-back direction.

[Feature A3]

The physical quantity measurement device according to Feature A1 or A2,wherein

the housing includes a front narrowed portion (111) forming the frontwall surface and bulges toward the back wall surface in the front-backdirection,

the front narrowed portion narrows the measurement flow path such that ameasurement width dimension (W1) that is a distance between the frontwall surface and the back wall surface in the front-back directiongradually decreases in a direction from upstream toward the physicalquantity sensor, and

the front distance is a distance between the physical quantity sensorand the front narrowed portion in the front-back direction.

[Feature A4]

The physical quantity measurement device according to Feature A3,wherein

the measurement flow path includes:

-   -   a measurement inlet (35) which is an upstream end of the        measurement flow path and through which the fluid flows into the        measurement flow path;    -   a measurement outlet (36) which is a downstream end of the        measurement flow path and through which the fluid flows out of        the measurement flow path,    -   a center line (CL4) of the measurement flow path extends along        the measurement flow path and passes through a center (CO2) of        the measurement inlet and a center (CO3) of the measurement        outlet,

the front narrowed portion has a front peak (111 a) at which a distance(W2) between the front narrowed portion and the center line of themeasurement flow path is the smallest in the measurement flow path,

the front narrowed portion is provided at a position where the frontpeak and the physical quantity sensor face each other in the front-backdirection, and

the front distance is a distance between the front peak and the physicalquantity sensor.

[Feature A5]

The physical quantity measurement device according to Feature A3 or A4,wherein

the housing includes a back narrowed portion (112) forming the back wallsurface and bulges toward the front wall surface in the front-backdirection, and

the back narrowed portion narrows the measurement flow path such thatthe measurement width dimension gradually decreases in the directionfrom upstream toward the physical quantity sensor.

[Feature A6]

The physical quantity measurement device according to any one ofFeatures A1 to A5, wherein

the measurement flow path includes a front region (122) which is aregion between the front wall surface and the support front surface inthe front-back direction,

the front region includes:

-   -   a floor region (122 a) between the physical quantity sensor and        the floor surface in the height direction; and    -   a ceiling region (122 b) opposite to the floor region across the        physical quantity sensor in the height direction,

a cross-sectional area (S1) of a portion of the measurement flow path inwhich the physical quantity sensor is provided includes:

-   -   a floor area (S2) which is an area of the floor region; and    -   a ceiling area (S3) which is an area of the ceiling region, and

the ceiling area is smaller than the floor area.

[Feature A7]

The physical quantity measurement device according to Feature A6,wherein

the measurement flow path is curved so that the floor surface becomes aninner curve of the measurement flow path, and

the floor region is provided between the inner curve and the ceilingregion in the front region.

[Feature A8]

The physical quantity measurement device according to any one ofFeatures A1 to A7, wherein

the physical quantity sensor includes:

-   -   a heater (71) that generates heat; and    -   a temperature detector (72, 73) that detects a temperature, the        temperature detector and the heater being arranged along one        surface (65 a) of the physical quantity sensor, and

the front distance is a distance between the front wall surface and theheater.

[Feature A9]

The physical quantity measurement device according to any one ofFeatures A1 to A7, wherein

the sensor support includes:

-   -   a sensor substrate (65) which is a substrate on which the        physical quantity sensor is mounted; and    -   a protective resin (55) formed of a resin material and        protecting the sensor substrate and the physical quantity        sensor, and

the protective resin forms the support front surface and the supportback surface.

<Features of Configuration Group B>

The configurations disclosed in the present specification include thefeatures of the configuration group B as described below.

[Feature B1]

A physical quantity measurement device (20, 200) for measuring aphysical quantity of a fluid, the physical quantity measurement devicecomprising:

a measurement flow path (32, 212) through which the fluid flows;

a detection unit (50, 220) including a physical quantity sensor (22,202) that is provided in the measurement flow path and detects thephysical quantity of the fluid, and a sensor support (51, 221) thatsupports the physical quantity sensor; and

a housing (21, 201) forming the measurement flow path and a containerspace (150, 290) that houses a part of the detection unit, wherein

an inner surface of the housing includes:

-   -   a housing intersecting surface (137, 277) that intersects an        arrangement direction (Y) in which the measurement flow path and        the container space are arranged;    -   a housing flow path surface (135, 275) extending from the        housing intersecting surface toward the measurement flow path;        and    -   a housing container surface (136, 276) extending from the        housing intersecting surface toward the container space,

the housing includes a housing partition (131, 271) provided on at leastone of the housing intersecting surface, the housing flow path surfaceand the housing container surface, and

the housing partition protrudes toward the detection unit and contactsthe detection unit between the housing and the detection unit such thatthe housing partition separates the measurement flow path and thecontainer space from each other.

[Feature B2]

The physical quantity measurement device according to Feature B1,wherein the housing partition makes a loop around the detection unit.

[Feature B3]

The physical quantity measurement device according to Feature B1 or B2,wherein the housing partition is arranged at a position on the housingintersecting surface closer to the housing flow path surface than to thehousing container surface.

[Feature B4]

The physical quantity measurement device according to any one ofFeatures B1 to B3, wherein

the housing intersecting surface and a center line (CL11) of the housingpartition provided on the housing intersecting surface intersect witheach other and form therebetween a container angle (θ12) facing thecontainer space and a flow path angle (θ11) facing the measurement flowpath, and

the container angle is larger than the flow path angle.

[Feature B5]

The physical quantity measurement device according to any one ofFeatures B1 to B4, wherein

the detection unit includes a unit recess (161) that is a recessprovided on the detection unit, and

the housing partition is inserted into the unit recess and is in contactwith an inner surface of the unit recess.

[Feature B6]

The physical quantity measurement device according to any one ofFeatures B1 to B5, wherein

an outer surface of the detection unit includes:

-   -   a unit intersecting surface (147, 287) that intersects the        arrangement direction (Y) in which the measurement flow path and        the container space are arranged;    -   a unit flow path surface (145, 285) extending from the unit        intersecting surface toward the measurement flow path; and    -   a unit container surface (146, 286) extending from the unit        intersecting surface toward the container space, and

the housing partition is in contact with at least one of the unitintersecting surface, the unit flow path surface and the unit containersurface.

[Feature B7]

The physical quantity measurement device according to Feature B6,wherein the housing partition is provided on the housing intersectingsurface and is in contact with the unit intersecting surface.

[Feature B8]

A physical quantity measurement device (20, 200) for measuring aphysical quantity of a fluid, the physical quantity measurement devicecomprising:

a measurement flow path (32, 212) through which the fluid flows;

a detection unit (50, 220) including a physical quantity sensor (22,202) that is provided in the measurement flow path and detects thephysical quantity of the fluid, and a sensor support (51, 221) thatsupports the physical quantity sensor; and

a housing (21, 201) forming the measurement flow path and a containerspace (150, 290) that houses a part of the detection unit, wherein

an outer surface of the detection unit includes:

-   -   a unit intersecting surface (147, 287) that intersects an        arrangement direction (Y) in which the measurement flow path and        the container space are arranged;    -   a unit flow path surface (145, 285) extending from the unit        intersecting surface toward the measurement flow path; and    -   a unit container surface (146, 286) extending from the unit        intersecting surface toward the container space,

the detection unit includes a unit partition (162, 302) provided on atleast one of the unit intersecting surface, the unit flow path surfaceand the unit container surface, and

the unit partition protrudes toward the housing and contacts the housingbetween the housing and the detection unit such that the unit partitionseparates the measurement flow path and the container space from eachother.

[Feature B9]

The physical quantity measurement device according to Feature B8,wherein the unit partition makes a loop around the detection unit.

[Feature B10]

The physical quantity measurement device according to Feature B8 or B9,wherein the unit partition is arranged at a position on the unitintersecting surface closer to the unit flow path surface than to theunit container surface.

[Feature B11]

The physical quantity measurement device according to any one ofFeatures B8 to B10, wherein

the unit intersecting surface and a center line (CL13) of the unitpartition provided on the unit intersecting surface intersect with eachother and form therebetween a container angle (θ14) facing the containerspace and a flow path angle (θ13) facing the measurement flow path, and

the container angle is larger than the flow path angle.

[Feature B12]

The physical quantity measurement device according to any one ofFeatures B8 to B11, wherein

the housing includes a housing recess (163) that is a recess provided onthe housing, and

the unit partition is inserted into the housing recess and is in contactwith an inner surface of the housing recess.

[Feature B14]

The physical quantity measurement device according to any one ofFeatures B8 to B13, wherein

an inner surface of the housing includes:

-   -   a housing intersecting surface (137, 277) that intersects the        arrangement direction (Y) in which the measurement flow path and        the container space are arranged;    -   a housing flow path surface (135, 275) extending from the        housing intersecting surface toward the measurement flow path;        and    -   a housing container surface (136, 276) extending from the        housing intersecting surface toward the container space, and

the unit partition is in contact with at least one of the housingintersecting surface, the housing flow path surface and the housingcontainer surface.

[Feature B15]

The physical quantity measurement device according to Feature B14,wherein the unit partition is provided on the unit intersecting surfaceand is in contact with the housing intersecting surface.

<Features of Configuration Group C>

The configurations disclosed in the present specification include thefeatures of the configuration group C as described below.

[Feature C1]

A physical quantity measurement device (20) for measuring a physicalquantity of a fluid, the physical quantity measurement devicecomprising:

a through flow path (31) including:

-   -   a through inlet (33) through which the fluid flows into the        through flow path; and    -   a through outlet (34) through which the fluid flowing from the        through inlet flows out of the through flow path;

a measurement flow path (32) branching from the through flow path formeasurement of the physical quantity of the fluid, the measurement flowpath (32) including:

-   -   a measurement inlet (35) which is provided between the through        inlet and the through outlet and through which the fluid flows        into the measurement flow path; and    -   a measurement outlet (36) through which the fluid flowing from        the measurement inlet flows out of the measurement flow path;

a physical quantity sensor (22) that is provided in the measurement flowpath and detects the physical quantity of the fluid; and

a housing (21) that forms the through flow path and the measurement flowpath, wherein

an inner surface of the housing includes:

-   -   an inlet ceiling surface (342) that defines an inlet through        path (331) which is between and connects the through inlet and        the measurement inlet in the through flow path, the inlet        ceiling surface being between and connecting the through inlet        and the measurement inlet in a direction (Z) in which the        through inlet and the through outlet are arranged; and    -   an inlet floor surface (346) that defines the inlet through path        and faces the inlet ceiling surface through the inlet through        path, and

the inlet ceiling surface includes a ceiling inclined surface (342, 342a) that extends from the through inlet toward the measurement inlet andis inclined with respect to the inlet floor surface such that a distance(H21) between the ceiling inclined surface and the inlet floor surfacegradually decreases in a direction from the through inlet toward thethrough outlet.

[Feature C2]

The physical quantity measurement device according to Feature C1,wherein an inclination angle (θ21) of the ceiling inclined surface withrespect to the inlet floor surface is larger than or equal to 10degrees.

[Feature C3]

The physical quantity measurement device according to Feature C1 or C2,wherein the ceiling inclined surface is inclined with respect to theinlet floor surface such that the ceiling inclined surface faces to thethrough inlet.

[Feature C4]

The physical quantity measurement device according to any one ofFeatures C1 to C3, wherein the ceiling inclined surface is inclined withrespect to a main flow direction (Z) which is a direction of a main flowof the fluid flowing into the through inlet such that the ceilinginclined surface faces to the through inlet.

[Feature C5]

The physical quantity measurement device according to Feature C4,wherein an inclination angle (θ22) of the ceiling inclined surface withrespect to the main flow direction is larger than or equal to 10degrees.

[Feature C6]

The physical quantity measurement device according to Feature C4 or C5,wherein

the housing includes an angle setting surface (27 a) that sets anattaching angle of the housing with respect to an attachment object (14)to which the housing is attached, and

the main flow direction is a direction in which the angle settingsurface extends.

[Feature C7]

The physical quantity measurement device according to any one ofFeatures C1 to C6, wherein a cross-sectional area (S21) of the inletthrough path gradually decreases in a direction from the through inlettoward the measurement inlet.

[Feature C8]

The physical quantity measurement device according to any one ofFeatures C1 to C7, wherein an inclination angle (θ25) of a center line(CL23) of the measurement flow path at the measurement inlet withrespect to an inlet through line (CL24) that is a center line of theinlet through path is larger than or equal to 90 degrees.

[Feature C9]

The physical quantity measurement device according to any one ofFeatures C1 to C8, wherein a branch angle (θ26) of the measurement flowpath with respect to the through flow path is smaller than or equal to60 degrees.

<Features of Configuration Group D>

The configurations disclosed in the present specification include thefeatures of the configuration group D as described below.

[Feature D1]

A physical quantity measurement device (20) for measuring a physicalquantity of a fluid, the physical quantity measurement devicecomprising:

a measurement flow path (32) including a measurement inlet (35) throughwhich the fluid flows into the measurement flow path, and a measurementoutlet (36) through which the fluid flowing from the measurement inletflows out of the measurement flow path;

a physical quantity sensor (22) that is provided in the measurement flowpath and detects the physical quantity of the fluid; and

a housing (21) that defines the measurement flow path, wherein

the measurement flow path includes a sensor path (405) in which thephysical quantity sensor is disposed;

an upstream curved path (406) provided between the sensor path and themeasurement inlet in the measurement flow path, the upstream curved pathbeing curved in the housing so as to extend from the sensor path towardthe measurement inlet; and

a downstream curved path (407) provided between the sensor path and themeasurement outlet in the measurement flow path, the downstream curvedpath being curved in the housing so as to extend from the sensor pathtoward the measurement outlet,

an inner surface of the housing includes:

-   -   an upstream outer curved surface (411) that defines an outer        outline of a curved part of the upstream curved path; and    -   a downstream outer curved surface (421) that defines an outer        outline of a curve part of the downstream curved path,

a degree of recess of the downstream outer curved surface in a directionexpanding the measurement flow path is larger than a degree of recess ofthe upstream outer curved surface in the direction expanding themeasurement flow path.

[Feature D2]

The physical quantity measurement device according to Feature D1,wherein

the upstream outer curved surface includes an upstream outer archedsurface (411) arched along the upstream curved path,

the downstream outer curved surface includes a downstream outer archedsurface (461) arched along the downstream curved path, and

a radius of curvature (R34) of the downstream outer arched surface issmaller than a radius of curvature (R33) of the upstream outer archedsurface such that the degree of recess of the downstream outer curvedsurface is larger than the degree of recess of the upstream outer curvedsurface.

[Feature D3]

The physical quantity measurement device according to Feature D1,wherein

the upstream outer curved surface includes an upstream outer archedsurface (411) arched along the upstream curved path, and

the downstream outer curved surface forms an internal corner (424) whichhas surfaces inwardly joined to each other to be recessed in thedownstream curved path such that the degree of recess of the downstreamouter curved surface is larger than the degree of recess of the upstreamouter curved surface.

[Feature D4]

The physical quantity measurement device according to any one ofFeatures D1 to D3, wherein

the inner surface of the housing includes:

-   -   an upstream inner curved surface (415) that defines an inner        outline of a curved part of the upstream curved path; and    -   a downstream inner curved surface (425) that defines an inner        outline of the curve part of the downstream curved path, and

in a direction orthogonal to a center line (CL4) of the measurement flowpath, a largest distance (L35 b) between the downstream outer curvedsurface and the downstream inner curved surface is larger than a largestdistance (L35 a) between the upstream outer curved surface and theupstream inner curved surface.

[Feature D5]

The physical quantity measurement device according to Feature D4,wherein a degree of protrusion of the downstream inner curved surface inthe direction expanding the measurement flow path is smaller than adegree of protrusion of the upstream inner curved surface in thedirection expanding the measurement flow path.

[Feature D6]

The physical quantity measurement device according to Feature D4 or D5,wherein

the upstream inner curved surface includes an upstream inner archedsurface (415) arched along the upstream curved path,

the downstream inner curved surface includes a downstream inner archedsurface (425) arched along the downstream curved path, and

a radius of curvature (R32) of the downstream inner arched surface islarger than a radius of curvature (R31) of the upstream inner archedsurface such that the degree of protrusion of the downstream innercurved surface is smaller than the degree of protrusion of the upstreaminner curved surface.

[Feature D7]

The physical quantity measurement device according to any one offeatures D1 to D6, wherein the sensor path extends in a direction (Z) inwhich the upstream curved path and the downstream curved path arearranged.

[Feature D8]

The physical quantity measurement device according to any one ofFeatures D1 to D7, wherein

the housing includes a measurement narrowed portion (111, 112) thatgradually reduces and narrows the measurement flow path in a directionfrom the measurement inlet toward the physical quantity sensor, andgradually expands the measurement flow path in a direction from thephysical quantity sensor toward the measurement outlet, and

the measurement narrowed portion is provided in the measurement flowpath between an upstream end part of the upstream curved path and adownstream end part of the downstream curved path.

[Feature D9]

The physical quantity measurement device according to Feature D8,wherein

the measurement narrowed portion includes:

-   -   a measurement narrowing surface (431, 441) that forms the inner        surface of the housing and gradually reduces and narrows the        measurement flow path in the direction from the measurement        inlet toward the physical quantity sensor; and    -   a measurement expanding surface (432, 442) that gradually        expands the measurement flow path in the direction from the        physical quantity sensor toward the measurement outlet, and

a length (W33 a, W33 b) of the measurement expanding surface is largerthan a length (W32 a, W32 b) of the measurement narrowing surface in anarrangement direction (Z) in which the upstream curved path and thedownstream curved path are arranged.

[Feature D10]

The physical quantity measurement device according to Feature D8 or D9,wherein the measurement expanding surface extends straight from thephysical quantity sensor toward the measurement outlet.

[Feature D11]

The physical quantity measurement device according to any one ofFeatures D8 to D10, wherein a distance (W34 a, W35 a) between thedownstream outer curved surface and the measurement narrowed portion inan arrangement direction (Z) in which the upstream curved path and thedownstream curved path are arranged is larger than a distance (W34 b,W35 b) between the upstream outer curved surface and the measurementnarrowed portion in the arrangement direction.

[Feature D12]

The physical quantity measurement device according to any one ofFeatures D8 to D11, wherein

the inner surface of the housing includes a pair of measurement wallsurfaces (103, 104) defining the measurement flow path and facing eachother across the upstream outer curved surface and the downstream outercurved surface, and

the measurement narrowed portion is provided on at least one of the pairof measurement wall surfaces.

[Feature D13]

The physical quantity measurement device according to any one ofFeatures D1 to D12, wherein

the inner surface of the housing includes a pair of wall surfaces (103,104) defining the measurement flow path and facing each other across theupstream outer curved surface and the downstream outer curved surface,and

the measurement outlet is provided on at least one of the pair of wallsurfaces such that the measurement flow path is open through themeasurement outlet in a direction (X) in which the pair of wall surfacesare arranged.

[Feature Da1]

A physical quantity measurement device (20) for measuring a physicalquantity of a fluid, the physical quantity measurement devicecomprising:

a measurement flow path (32) including a measurement inlet (35) throughwhich the fluid flows into the measurement flow path, and a measurementoutlet (36) through which the fluid flowing from the measurement inletflows out of the measurement flow path;

a physical quantity sensor (22) that is provided in the measurement flowpath and detects the physical quantity of the fluid; and

a housing (21) that defines the measurement flow path, wherein

the measurement flow path includes

-   -   a sensor path (405) in which the physical quantity sensor is        disposed;    -   an upstream curved path (406) provided between the sensor path        and the measurement inlet in the measurement flow path, the        upstream curved path being curved in the housing so as to extend        from the sensor path toward the measurement inlet; and    -   a downstream curved path (407) provided between the sensor path        and the measurement outlet in the measurement flow path, the        downstream curved path being curved in the housing so as to        extend from the sensor path toward the measurement outlet,

the inner surface of the housing includes

-   -   an upstream outer curved surface (411) that defines an outer        outline of a curved part of the upstream curved path; and    -   a downstream outer curved surface (421) that defines an outer        outline of a curve part of the downstream curved path,

an arrangement line (CL31) is defined as an imaginary straight line thatpasses through the physical quantity sensor and extends in anarrangement direction (Z) in which the upstream curved path and thedownstream curved path are arranged, and

a distance (L31 b) on the arrangement line between the downstream outercurved surface and the physical quantity sensor is larger than adistance (L31 a) on the arrangement line between the upstream outercurved surface and the physical quantity sensor.

[Feature Da2]

The physical quantity measurement device according to Feature Da1,wherein the sensor path extends along the arrangement line.

[Feature Da3]

The physical quantity measurement device according to Feature Da1 orDa2, wherein, in the sensor path, a distance (L34 b) between thephysical quantity sensor and the downstream curved path is larger thanthe distance (L34 a) between the physical quantity sensor and theupstream curved path.

[Feature Da4]

The physical quantity measurement device according to any one ofFeatures Da1 to Da3, further comprising a sensor support (51) supportingthe physical quantity sensor in the measurement flow path, wherein

a distance (L32 b) on the arrangement line between the downstream outercurved surface and the sensor support is larger than a distance (L32 a)on the arrangement line between the upstream outer curved surface andthe sensor support.

[Feature Da5]

The physical quantity measurement device according to any one ofFeatures Da1 to Da4, wherein the downstream outer curved surfaceincludes a downstream outer vertical surface (423) provided at aposition through which the arrangement line passes, the downstream outervertical surface extending straight upstream from a downstream end partof the downstream curved path.

[Feature Da6]

The physical quantity measurement device according to any one ofFeatures Da1 to Da5, wherein

the inner surface of the housing includes a downstream inner curvedsurface (425) that defines an inner outline of the curve part of thedownstream curved path, and

the downstream inner curved surface includes a downstream inner archedsurface (425) which is arched along the downstream curved path.

[Feature Da7]

The physical quantity measurement device according to any one ofFeatures Da1 to Da6, wherein

the housing includes a measurement narrowed portion (111, 112) thatgradually reduces and narrows the measurement flow path in a directionfrom the measurement inlet toward the physical quantity sensor, andgradually expands the measurement flow path in a direction from thephysical quantity sensor toward the measurement outlet, and

the measurement narrowed portion is provided in the measurement flowpath between an upstream end part of the upstream curved path and adownstream end part of the downstream curved path.

[Feature Da8]

The physical quantity measurement device according to Feature Da7,wherein

the measurement narrowed portion includes:

-   -   a measurement narrowing surface (431, 441) that forms the inner        surface of the housing and gradually reduces and narrows the        measurement flow path in the direction from the measurement        inlet toward the physical quantity sensor; and    -   a measurement expanding surface (432, 442) that gradually        expands the measurement flow path in the direction from the        physical quantity sensor toward the measurement outlet, and

a length (W33 a, W33 b) of the measurement expanding surface in thearrangement direction is larger than a length (W32 a, W32 b) of themeasurement narrowing surface in the arrangement direction.

[Feature Da9]

The physical quantity measurement device according to Feature Da8,wherein the measurement expanding surface extends straight from thephysical quantity sensor toward the measurement outlet.

[Feature Da10]

The physical quantity measurement device according to any one ofFeatures Da7 to Da9, wherein a distance (W34 a, W35 a) between thedownstream outer curved surface and the measurement narrowed portion onthe arrangement line is larger than a distance (W34 b, W35 b) betweenthe upstream outer curved surface and the measurement narrowed portionon the arrangement line.

[Feature Da11]

The physical quantity measurement device according to any one ofFeatures Da7 to Da10, wherein

the inner surface of the housing includes a pair of measurement wallsurfaces (103, 104) defining the measurement flow path and facing eachother across the upstream outer curved surface and the downstream outercurved surface, and

the measurement narrowed portion is provided on at least one of the pairof measurement wall surfaces.

[Feature Da12]

The physical quantity measurement device according to any one ofFeatures Da1 to Da11, wherein the upstream outer curved surface includesan upstream outer arched surface (411) which is arched along theupstream curved path and connects an upstream end part of the upstreamcurved path and a downstream end part of the upstream curved path.

[Feature Da13]

The physical quantity measurement device according to any one ofFeatures Da1 to Da12, wherein the inner surface of the housing includesan inner measurement curved surface (402) that is curved to bulge towardthe physical quantity sensor and connects the measurement inlet and themeasurement outlet, the inner measurement curved surface defining aninner outline of a curved part of the measurement flow path.

[Feature Da14]

The physical quantity measurement device according to any one ofFeatures Da1 to Da13, wherein

the inner surface of the housing includes a pair of wall surfaces (103,104) defining the measurement flow path and facing each other across theupstream outer curved surface and the downstream outer curved surface,and

the measurement outlet is provided on at least one of the pair of wallsurfaces such that the measurement flow path is open through themeasurement outlet in an orthogonal direction (X) which is orthogonal tothe arrangement line and in which the pair of wall surfaces face eachother.

<Features of Configuration Group E>

The configurations disclosed in the present specification include thefeatures of the configuration group E as described below.

[Feature E1]

A physical quantity measurement device (20) for measuring a physicalquantity of a fluid, the physical quantity measurement devicecomprising:

a measurement flow path (32) including a measurement inlet (35) throughwhich the fluid flows into the measurement flow path, and a measurementoutlet (36) through which the fluid flowing from the measurement inletflows out of the measurement flow path;

a physical quantity sensor (22) that is provided in the measurement flowpath and detects the physical quantity of the fluid; and

a sensor support (51) supporting the physical quantity sensor in themeasurement flow path; and

a housing (21) that defines the measurement flow path, wherein

the measurement flow path includes

-   -   a sensor path (405) in which the physical quantity sensor is        disposed;    -   an upstream curved path (406) provided between the sensor path        and the measurement inlet in the measurement flow path, the        upstream curved path being curved in the housing so as to extend        from the sensor path toward the measurement inlet; and    -   a downstream curved path (407) provided between the sensor path        and the measurement outlet in the measurement flow path, the        downstream curved path being curved in the housing so as to        extend from the sensor path toward the measurement outlet,

the housing includes a measurement narrowed portion (111, 112) thatgradually reduces and narrows the measurement flow path in a directionfrom the measurement inlet toward the physical quantity sensor,

an arrangement line (CL31) is defined as an imaginary straight line thatpasses through the physical quantity sensor and extends in anarrangement direction (Z) in which the upstream curved path and thedownstream curved path are arranged, and

an upstream end (55 c, 471) of the sensor support is provided upstreamof the measurement narrowed portion in an arrangement cross section(CS41) along the arrangement line.

[Feature E2]

The physical quantity measurement device according to Feature E1,wherein the upstream end of the sensor support includes an upstreaminclined portion (471) that is inclined with respect to the arrangementcross section and extends across an upstream end of the measurementnarrowed portion in the arrangement direction.

[Feature E3]

The physical quantity measurement device according to Feature E1 or E2,wherein a downstream end (55 d, 472) of the sensor support is providedupstream of a downstream end (111 c, 112 c) of the measurement narrowedportion in the arrangement cross section.

[Feature E4]

The physical quantity measurement device according to Feature E3,wherein a downstream end of the sensor support includes a downstreaminclined portion (472) that is inclined with respect to the arrangementcross section and extends across a downstream end of the measurementnarrowed portion in the arrangement direction.

[Feature E5]

The physical quantity measurement device according to any one ofFeatures E1 to E4, wherein

the measurement narrowed portion includes:

-   -   a measurement narrowing surface (431, 441) that forms an inner        surface of the housing and gradually reduces and narrows the        measurement flow path in the direction from the measurement        inlet toward the physical quantity sensor; and    -   a measurement expanding surface (432, 442) that gradually        expands the measurement flow path in a direction from the        physical quantity sensor toward the measurement outlet, and

a length (W33 a, W33 b) of the measurement expanding surface in thearrangement direction is larger than a length (W32 a, W32 b) of themeasurement narrowing surface in the arrangement direction.

[Feature E6]

The physical quantity measurement device according to any one ofFeatures E1 to E5, wherein

the physical quantity sensor is mounted on a front surface (55 e) whichis one surface of the sensor support,

an inner surface of the housing includes a pair of wall surfaces whichform the measurement flow path and face each other across the sensorsupport, the pair of wall surfaces are:

-   -   a front measurement wall surface (103) facing the front surface        of the sensor support; and    -   a back measurement wall surface (104) facing a back surface (55        f) of the sensor support behind the front surface, and

the housing includes a front narrowed portion (111) as the measurementnarrowed portion, positioned on the front measurement wall surface so asto face the physical quantity sensor.

[Feature E7]

The physical quantity measurement device according to Feature E6,wherein the housing includes a back narrowed portion (112) as themeasurement narrowed portion, positioned on the back measurement wallsurface so as to opposite to the front narrowed portion across thephysical quantity sensor.

[Feature E8]

The physical quantity measurement device according to Feature E7,wherein a distance (D33 a) between the sensor support and the frontnarrowed portion is smaller than a distance (D33 b) between the sensorsupport and the back narrowed portion in the arrangement cross section.

[Feature E9]

The physical quantity measurement device according to Feature E7 or E8,wherein

a center line (CL4) of the measurement flow path extends along themeasurement flow path and passes through a center (CO2) of themeasurement inlet and a center (CO3) of the measurement outlet,

the front narrowed portion includes a front peak (111 a) as a peak atwhich a distance (W2) between the front narrowed portion and the centerline of the measurement flow path is the smallest in the measurementflow path,

the back narrowed portion includes a back peak (112 a) as a peak atwhich a distance (W3) between the back narrowed portion and the centerline of the measurement flow path is the smallest in the measurementflow path, and

a reduction rate at which the front narrowed portion reduces themeasurement flow path is larger than a reduction rate at which the backnarrowed portion reduces the measurement flow path.

[Feature E10]

The physical quantity measurement device according to any one ofFeatures E1 to E9, wherein the physical quantity sensor is provided inthe measurement flow path in accordance with a position at which a flowvelocity is maximized by the measurement narrowed portion narrowing themeasurement flow path.

[Feature E11]

The physical quantity measurement device according to any one ofFeatures E1 to E10, wherein the upstream end of the sensor support isprovided in the upstream curved path in the arrangement cross section.

[Feature E12]

The physical quantity measurement device according to any one ofFeatures E1 to E11, wherein an opening area of the measurement outlet issmaller than an opening area of the measurement inlet.

[Feature E13]

The physical quantity measurement device according to any one ofFeatures E1 to E12, further comprising a through flow path (31)including a through inlet (33) through which the fluid flows into thethrough flow path, and a through outlet (34) through which the fluidflowing from the through inlet flows out of the through flow path,wherein

the measurement flow path is a branch flow path branched from thethrough flow path, and

an opening area of the through outlet is smaller than an opening area ofthe through inlet.

<Features of Configuration Group Z>

The configurations disclosed in the present specification include thefeatures of the configuration group Z as described below.

[Feature Z1]

A physical quantity measurement device (20) for measuring a physicalquantity of a fluid, the physical quantity measurement devicecomprising:

a measurement flow path (32) including a measurement inlet (35) throughwhich the fluid flows into the measurement flow path, and a measurementoutlet (36) through which the fluid flowing from the measurement inletflows out of the measurement flow path;

a physical quantity sensor (22) that is provided in the measurement flowpath and detects the physical quantity of the fluid; and

a housing (21) that defines the measurement flow path.

According to this feature Z1, the physical quantity can be detected bythe physical quantity sensor for the fluid flowing from the measurementinlet to the measurement flow path. Among the configurations disclosedin the present specification, configurations not included in the FeatureZ1 are not essential. Although some problems are described in thisspecification, the Feature Z1 is a necessary configuration for solvingthese problems.

While the present disclosure has been described with reference toembodiments thereof, it is to be understood that the disclosure is notlimited to the embodiments and constructions. To the contrary, thepresent disclosure is intended to cover various modification andequivalent arrangements. In addition, while the various elements areshown in various combinations and configurations, which are exemplary,other combinations and configurations, including more, less or only asingle element, are also within the spirit and scope of the presentdisclosure.

What is claimed is:
 1. A physical quantity measurement device formeasuring a physical quantity of a fluid, the physical quantitymeasurement device comprising: a measurement flow path including ameasurement inlet through which the fluid flows into the measurementflow path, and a measurement outlet through which the fluid flowing fromthe measurement inlet flows out of the measurement flow path; a physicalquantity sensor that is provided in the measurement flow path anddetects the physical quantity of the fluid; a sensor support supportingthe physical quantity sensor in the measurement flow path; a throughflow path including a through inlet through which the fluid flows intothe through flow path, and a through outlet through which the fluidflowing from the through inlet flows out of the through flow path; and ahousing that defines the measurement flow path and the through flowpath, wherein the measurement flow path includes: a sensor path in whichthe physical quantity sensor is disposed; an upstream curved pathprovided between the sensor path and the measurement inlet in themeasurement flow path, the upstream curved path being curved in thehousing so as to extend from the sensor path toward the measurementinlet; and a downstream curved path provided between the sensor path andthe measurement outlet in the measurement flow path, the downstreamcurved path being curved in the housing so as to extend from the sensorpath toward the measurement outlet, the housing includes a measurementnarrowed portion that gradually reduces and narrows the measurement flowpath in a direction from the measurement inlet toward the physicalquantity sensor, an arrangement line is defined as an imaginary straightline that passes through the physical quantity sensor and extends in anarrangement direction in which the upstream curved path and thedownstream curved path are arranged, an upstream end of the sensorsupport is provided upstream of the measurement narrowed portion in anarrangement cross section along the arrangement line, the measurementflow path is a branch flow path branched from the through flow path, anopening area of the through outlet is smaller than an opening area ofthe through inlet, and a downstream end of the sensor support isprovided upstream of a downstream end of the measurement narrowedportion in the arrangement cross section.
 2. The physical quantitymeasurement device according to claim 1, wherein the upstream end of thesensor support includes an upstream inclined portion that is inclinedwith respect to the arrangement cross section and extends across anupstream end of the measurement narrowed portion in the arrangementdirection.
 3. The physical quantity measurement device according toclaim 1, wherein the downstream end of the sensor support includes adownstream inclined portion that is inclined with respect to thearrangement cross section and extends across a downstream end of themeasurement narrowed portion in the arrangement direction.
 4. Thephysical quantity measurement device according to claim 1, wherein themeasurement narrowed portion includes: a measurement narrowing surfacethat forms an inner surface of the housing and gradually reduces andnarrows the measurement flow path in the direction from the measurementinlet toward the physical quantity sensor; and a measurement expandingsurface that gradually expands the measurement flow path in a directionfrom the physical quantity sensor toward the measurement outlet, and alength of the measurement expanding surface in the arrangement directionis larger than a length of the measurement narrowing surface in thearrangement direction.
 5. The physical quantity measurement deviceaccording to claim 1, wherein the physical quantity sensor is mounted ona front surface which is one surface of the sensor support, an innersurface of the housing includes a pair of wall surfaces which form themeasurement flow path and face each other across the sensor support, thepair of wall surfaces are: a front measurement wall surface facing thefront surface of the sensor support; and a back measurement wall surfacefacing a back surface of the sensor support behind the front surface,and the housing includes a front narrowed portion as the measurementnarrowed portion, positioned on the front measurement wall surface so asto face the physical quantity sensor.
 6. The physical quantitymeasurement device according to claim 5, wherein the housing includes aback narrowed portion as the measurement narrowed portion, positioned onthe back measurement wall surface so as to be positioned opposite to thefront narrowed portion across the physical quantity sensor.
 7. Thephysical quantity measurement device according to claim 6, wherein adistance between the sensor support and the front narrowed portion issmaller than a distance between the sensor support and the back narrowedportion in the arrangement cross section.
 8. The physical quantitymeasurement device according to claim 6, wherein a center line of themeasurement flow path extends along the measurement flow path and passesthrough a center of the measurement inlet and a center of themeasurement outlet, the front narrowed portion includes a front peak asa peak at which a distance between the front narrowed portion and thecenter line of the measurement flow path is the smallest in themeasurement flow path, the back narrowed portion includes a back peak asa peak at which a distance between the back narrowed portion and thecenter line of the measurement flow path is the smallest in themeasurement flow path, and a reduction rate at which the front narrowedportion reduces the measurement flow path is larger than a reductionrate at which the back narrowed portion reduces the measurement flowpath.
 9. The physical quantity measurement device according to claim 1,wherein the physical quantity sensor is provided in the measurement flowpath in accordance with a position at which a flow velocity is maximizedby the measurement narrowed portion narrowing the measurement flow path.10. The physical quantity measurement device according to claim 1,wherein the upstream end of the sensor support is provided in theupstream curved path in the arrangement cross section.
 11. The physicalquantity measurement device according to claim 1, wherein an openingarea of the measurement outlet is smaller than an opening area of themeasurement inlet.
 12. The physical quantity measurement deviceaccording to claim 1, wherein an upstream end surface of the sensorsupport includes an upstream inclined surface extending straight andoblique to the arrangement cross section, the measurement narrowedportion includes a front narrowed portion and a back narrowed portionwhich face each other across the sensor support and protrude to eachother to gradually narrow the measurement flow path, and in thearrangement cross section, a distance between the upstream inclinedsurface and the front narrowed portion is same along the arrangementline as a distance between the upstream inclined surface and the backnarrowed portion.
 13. The physical quantity measurement device accordingto claim 1, wherein a downstream end surface of the sensor supportincludes a downstream inclined surface extending straight and oblique tothe arrangement cross section, the measurement narrowed portion includesa front narrowed portion and a back narrowed portion which face eachother across the sensor support and protrude to each other to graduallynarrow the measurement flow path, and in the arrangement cross section,the downstream inclined surface is separated from the front narrowedportion along the arrangement line, and the downstream inclined surfaceis separated from the back narrowed portion along the arrangement line.14. The physical quantity measurement device according to claim 13,wherein in the arrangement cross section, a distance between thedownstream inclined surface and the front narrowed portion is same alongthe arrangement line as a distance between the downstream inclinedsurface and the back narrowed portion.